{"id":4002,"date":"2026-05-21T07:03:15","date_gmt":"2026-05-21T06:03:15","guid":{"rendered":"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel-international\/topic-1-formulae-equations-and-amount-of-substance\/empirical-and-molecular-formulae\/"},"modified":"2026-05-26T06:09:17","modified_gmt":"2026-05-26T05:09:17","slug":"empirical-and-molecular-formulae","status":"publish","type":"page","link":"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel-international\/topic-1-formulae-equations-and-amount-of-substance\/empirical-and-molecular-formulae\/","title":{"rendered":"Empirical and Molecular Formulae"},"content":{"rendered":"\n<section class=\"ols-revision-page ols-empirical-molecular-formulae-landing-page\">\n  <style>\n    .ols-revision-page {\n      --navy: #1C244B;\n      --blue: #2563eb;\n      --soft-blue: #eef4ff;\n      --soft-red: #fff7f7;\n      --soft-purple: #f7f0ff;\n      --soft-green: #f0f7f1;\n   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flex-start; padding: 22px 18px; border-radius: 22px; }\n      .ols-author-avatar-img { width: 72px; height: 72px; }\n      .ols-author-title { font-size: 24px; }\n      .ols-author-description { font-size: 15px; }\n      .ols-ert-card { min-height: 255px; }\n    }\n  \n  <\/style>\n\n  <aside class=\"ols-sidebar\">\r\n  <div class=\"ols-sidebar-header\">\r\n    <h3>Revision Notes<\/h3>\r\n    <p>A Level Chemistry<\/p>\r\n  <\/div>\r\n\r\n  <div class=\"ols-topic-group\">\r\n    <h4>Topic 1 Formulae, Equations and Amount of Substance<\/h4>\r\n\r\n    <ul class=\"ols-topic-list\">\r\n      <li>\r\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel-international\/topic-1-formulae-equations-and-amount-of-substance\/atoms-elements-and-molecules\/\">Atoms, Elements and Molecules<\/a>\r\n      <\/li>\r\n\r\n      <li>\r\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel-international\/topic-1-formulae-equations-and-amount-of-substance\/equations-and-reaction-types\/\">Equations and Reaction Types<\/a>\r\n\r\n        <ul class=\"ols-subtopic-list\">\r\n          <li>\r\n            <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel-international\/topic-1-formulae-equations-and-amount-of-substance\/equations-and-reaction-types\/writing-chemical-equations\/\">Writing Chemical Equations<\/a>\r\n          <\/li>\r\n          <li>\r\n            <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel-international\/topic-1-formulae-equations-and-amount-of-substance\/equations-and-reaction-types\/typical-reactions-of-acids\/\">Typical Reactions of Acids<\/a>\r\n          <\/li>\r\n          <li>\r\n            <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel-international\/topic-1-formulae-equations-and-amount-of-substance\/equations-and-reaction-types\/ionic-equations\/\">Ionic Equations<\/a>\r\n          <\/li>\r\n        <\/ul>\r\n      <\/li>\r\n\r\n      <li>\r\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel-international\/topic-1-formulae-equations-and-amount-of-substance\/mole-calculations\/\">Mole Calculations<\/a>\r\n\r\n        <ul class=\"ols-subtopic-list\">\r\n          <li>\r\n            <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel-international\/topic-1-formulae-equations-and-amount-of-substance\/mole-calculations\/comparing-masses-of-substances\/\">Comparing Masses of Substances<\/a>\r\n          <\/li>\r\n          <li>\r\n            <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel-international\/topic-1-formulae-equations-and-amount-of-substance\/mole-calculations\/calculations-involving-moles\/\">Calculations involving Moles<\/a>\r\n          <\/li>\r\n          <li>\r\n            <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel-international\/topic-1-formulae-equations-and-amount-of-substance\/mole-calculations\/calculations-using-reacting-masses\/\">Calculations using Reacting Masses<\/a>\r\n          <\/li>\r\n          <li>\r\n            <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel-international\/topic-1-formulae-equations-and-amount-of-substance\/mole-calculations\/the-yield-of-a-reaction\/\">The Yield of a Reaction<\/a>\r\n          <\/li>\r\n          <li>\r\n            <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel-international\/topic-1-formulae-equations-and-amount-of-substance\/mole-calculations\/atom-economy\/\">Atom Economy<\/a>\r\n          <\/li>\r\n        <\/ul>\r\n      <\/li>\r\n\r\n      <li>\r\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel-international\/topic-1-formulae-equations-and-amount-of-substance\/empirical-and-molecular-formulae\/\">Empirical and Molecular Formulae<\/a>\r\n\r\n        <ul class=\"ols-subtopic-list\">\r\n          <li>\r\n            <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel-international\/topic-1-formulae-equations-and-amount-of-substance\/empirical-and-molecular-formulae\/empirical-formulae\/\">Empirical Formulae<\/a>\r\n          <\/li>\r\n          <li>\r\n            <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel-international\/topic-1-formulae-equations-and-amount-of-substance\/empirical-and-molecular-formulae\/molecular-formulae\/\">Molecular Formulae<\/a>\r\n          <\/li>\r\n        <\/ul>\r\n      <\/li>\r\n\r\n      <li>\r\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel-international\/topic-1-formulae-equations-and-amount-of-substance\/calculations-with-solutions-and-gases\/\">Calculations with Solutions and Gases<\/a>\r\n\r\n        <ul class=\"ols-subtopic-list\">\r\n          <li>\r\n            <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel-international\/topic-1-formulae-equations-and-amount-of-substance\/calculations-with-solutions-and-gases\/molar-volume-calculations\/\">Molar Volume Calculations<\/a>\r\n          <\/li>\r\n          <li>\r\n            <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel-international\/topic-1-formulae-equations-and-amount-of-substance\/calculations-with-solutions-and-gases\/concentrations-of-solutions\/\">Concentrations of Solutions<\/a>\r\n          <\/li>\r\n          <li>\r\n            <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel-international\/topic-1-formulae-equations-and-amount-of-substance\/calculations-with-solutions-and-gases\/concentrations-in-ppm\/\">Concentrations in PPM<\/a>\r\n          <\/li>\r\n        <\/ul>\r\n      <\/li>\r\n    <\/ul>\r\n  <\/div>\r\n\r\n  <div class=\"ols-topic-group\">\r\n    <h4>Next Topics<\/h4>\r\n\r\n    <ul class=\"ols-topic-list\">\r\n      <li>\r\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel-international\/topic-2-atomic-structure-and-the-periodic-table\/\">Atomic Structure and The Periodic Table<\/a>\r\n      <\/li>\r\n      <li>\r\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel-international\/topic-3-bonding-structure\/\">Bonding &amp; Structure<\/a>\r\n      <\/li>\r\n      <li>\r\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel-international\/topic-4-organic-chemistry-and-alkanes\/\">Organic Chemistry &amp; Alkanes<\/a>\r\n      <\/li>\r\n    <\/ul>\r\n  <\/div>\r\n<\/aside>\r\n\r\n<script>\r\n(function() {\r\n  function normalisePath(path) {\r\n    return String(path || '')\r\n      .split('?')[0]\r\n      .split('#')[0]\r\n      .replace(\/\\\/+$|\\s+$\/g, '')\r\n      .toLowerCase();\r\n  }\r\n\r\n  function highlightActive() {\r\n    var sidebar = document.querySelector('.ols-sidebar');\r\n    if (!sidebar) return false;\r\n\r\n    var currentPath = normalisePath(window.location.pathname);\r\n    var links = sidebar.querySelectorAll('a[href]');\r\n  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{\r\n          matchedLi.classList.add('parent-active', 'active-main');\r\n          matched.setAttribute('aria-current', 'page');\r\n          matched.setAttribute('tabindex', '-1');\r\n          matched.setAttribute('data-ols-disabled-parent', '1');\r\n        }\r\n      }\r\n    }\r\n\r\n    return true;\r\n  }\r\n\r\n  if (!highlightActive()) {\r\n    document.addEventListener('DOMContentLoaded', highlightActive);\r\n  }\r\n})();\r\n<\/script>\r\n\n\n  <main class=\"ols-main\">\n      <nav class=\"ols-breadcrumbs\" aria-label=\"Breadcrumb\">\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/\">Revision Notes<\/a> \/\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/\">A Level Chemistry<\/a> \/\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel-international\/\">Edexcel International<\/a> \/\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel-international\/topic-1-formulae-equations-and-amount-of-substance\/\">Topic 1 Formulae, Equations and Amount of Substance<\/a> \/\n        <span>Empirical and Molecular Formulae<\/span>\n      <\/nav>\n\n      <header class=\"ols-title-card\">\n        <h1>Empirical and Molecular Formulae<\/h1>\n        <p class=\"ols-page-intro\">Use this landing page to move quickly between the key empirical and molecular formulae revision pages for Topic 1. Each card links to a focused page covering the simplest whole-number ratio of atoms and how to use molar mass to find the actual molecular formula.<\/p>\n\n        <div class=\"ols-badges\">\n          <div class=\"ols-badge\">Exam board: Edexcel International<\/div>\n          <div class=\"ols-badge\">Topic 1: Formulae, Equations and Amount of Substance<\/div>\n          <div class=\"ols-badge\">Level: A Level Chemistry<\/div>\n        <\/div>\n\n        <div class=\"ols-author\">\n          <img decoding=\"async\" class=\"ols-author-avatar-img\" src=\"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-content\/uploads\/2026\/05\/Author-Profile.jpeg\" alt=\"Dr. Mohammed Al-Fatah\">\n\n          <div class=\"ols-author-content\">\n            <h2 class=\"ols-author-title\">Written by:<br><span>Dr. Mohammed Al-Fatah<\/span><\/h2>\n            <p class=\"ols-author-description\">Chemistry specialist revision notes for A Level Chemistry.<\/p>\n\n            <a class=\"ols-linkedin-pill\" href=\"https:\/\/www.linkedin.com\/in\/doctormohammedfatah\/\" target=\"_blank\" rel=\"noopener noreferrer\">\n              <svg class=\"ols-linkedin-icon\" viewBox=\"0 0 24 24\" fill=\"currentColor\" aria-hidden=\"true\">\n                <path d=\"M4.98 3.5C4.98 4.88 3.86 6 2.48 6S0 4.88 0 3.5 1.12 1 2.48 1s2.5 1.12 2.5 2.5zM.5 8h4V24h-4V8zm7 0h3.8v2.2h.1c.5-.9 1.8-2.2 3.9-2.2 4.2 0 5 2.8 5 6.4V24h-4v-7.6c0-1.8 0-4.2-2.6-4.2s-3 2-3 4v7.8h-4V8z\"><\/path>\n              <\/svg>\n              View LinkedIn Profile\n            <\/a>\n          <\/div>\n        <\/div>\n      <\/header>\n\n      <article class=\"ols-note-card soft\">\n        <div class=\"ols-note-title\">\n          <div class=\"ols-note-icon\">1<\/div>\n          <h2>Choose an Empirical and Molecular Formulae Page<\/h2>\n        <\/div>\n\n        <p>Empirical and molecular formulae connect experimental composition data with the actual formula of a compound. These pages build from finding the simplest whole-number ratio of atoms through to using relative molecular mass to scale up to the true molecular formula.<\/p>\n\n        <div class=\"ols-key-box\">\n          <p><strong>Key idea:<\/strong> The empirical formula gives the simplest whole-number ratio of atoms in a compound, while the molecular formula gives the actual number of each type of atom in one molecule.<\/p>\n        <\/div>\n\n        <div class=\"ols-ert-grid\">\n          <a class=\"ols-ert-card\" href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel-international\/topic-1-formulae-equations-and-amount-of-substance\/empirical-and-molecular-formulae\/empirical-formulae\/\">\n            <div class=\"ols-ert-visual\">\n              <div class=\"ols-ert-icon ols-ert-empirical\" aria-hidden=\"true\">\n                <span class=\"ols-ert-box e1\">C<\/span>\n                <span class=\"ols-ert-box e2\">H<\/span>\n                <span class=\"ols-ert-box e3\">O<\/span>\n                <span class=\"ols-ert-label-mini\">simplest ratio<\/span>\n              <\/div>\n            <\/div>\n            <h3>Empirical Formulae<\/h3>\n            <p>Revise how to convert masses, percentages or combustion data into mole ratios and then into the simplest whole-number formula.<\/p>\n            <span class=\"ols-ert-meta\">Open revision page<\/span>\n          <\/a>\n\n          <a class=\"ols-ert-card\" href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel-international\/topic-1-formulae-equations-and-amount-of-substance\/empirical-and-molecular-formulae\/molecular-formulae\/\">\n            <div class=\"ols-ert-visual\">\n              <div class=\"ols-ert-icon ols-ert-molecular\" aria-hidden=\"true\">\n                <span class=\"ols-ert-box m1\">EF<\/span>\n                <span class=\"ols-ert-box m2\">\u00d7n<\/span>\n                <span class=\"ols-ert-box m3\">MF<\/span>\n                <span class=\"ols-ert-arrow\"><\/span>\n              <\/div>\n            <\/div>\n            <h3>Molecular Formulae<\/h3>\n            <p>Learn how the empirical formula mass and relative molecular mass are used to find the molecular formula of a compound.<\/p>\n            <span class=\"ols-ert-meta\">Open revision page<\/span>\n          <\/a>\n        <\/div>\n      <\/article>\n\n      <article class=\"ols-note-card purple\">\n        <div class=\"ols-note-title\">\n          <div class=\"ols-note-icon\">\u2713<\/div>\n          <h2>How to Use These Pages<\/h2>\n        <\/div>\n\n        <p>Start with empirical formulae so that you can confidently convert composition data into a ratio of moles. Then move to molecular formulae, where the empirical formula is treated as a repeat unit and scaled using the relative molecular mass.<\/p>\n\n        <div class=\"ols-key-box\">\n          <p><strong>Exam focus:<\/strong> In empirical formula calculations, divide each amount in moles by the smallest value before converting to whole numbers. In molecular formula calculations, compare the relative molecular mass with the empirical formula mass.<\/p>\n        <\/div>\n      <\/article>\n\n      <section class=\"ols-related-card\">\n        <h2>Related Topic 1 Pages<\/h2>\n        <p>Use these pages to connect empirical and molecular formulae with formulae, equations, mole calculations and later solution or gas calculations.<\/p>\n\n        <div class=\"ols-related-grid\">\n          <a class=\"ols-related-item\" href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel-international\/topic-1-formulae-equations-and-amount-of-substance\/atoms-elements-and-molecules\/\">Atoms, Elements and Molecules<\/a>\n          <a class=\"ols-related-item\" href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel-international\/topic-1-formulae-equations-and-amount-of-substance\/equations-and-reaction-types\/\">Equations and Reaction Types<\/a>\n          <a class=\"ols-related-item\" href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel-international\/topic-1-formulae-equations-and-amount-of-substance\/mole-calculations\/\">Mole Calculations<\/a>\n          <a class=\"ols-related-item\" href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel-international\/topic-1-formulae-equations-and-amount-of-substance\/empirical-and-molecular-formulae\/empirical-formulae\/\">Empirical Formulae<\/a>\n          <a class=\"ols-related-item\" href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel-international\/topic-1-formulae-equations-and-amount-of-substance\/empirical-and-molecular-formulae\/molecular-formulae\/\">Molecular Formulae<\/a>\n          <a class=\"ols-related-item\" href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel-international\/topic-1-formulae-equations-and-amount-of-substance\/calculations-with-solutions-and-gases\/\">Calculations with Solutions and Gases<\/a>\n        <\/div>\n      <\/section>\n\n      <section class=\"ols-attribution-card\">\n        <p><strong>Copyright notice:<\/strong> This revision page, including its written explanations, layout and teaching sequence, is produced for Online Learning System by Dr. Mohammed Al-Fatah. It is intended for student revision and may not be copied, redistributed or republished without permission.<\/p>\n      <\/section>\n\n      <script type=\"application\/ld+json\">\n      {\n        \"@context\": \"https:\/\/schema.org\",\n        \"@graph\": [\n          {\n            \"@type\": \"WebPage\",\n            \"@id\": \"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel-international\/topic-1-formulae-equations-and-amount-of-substance\/empirical-and-molecular-formulae\/#webpage\",\n            \"url\": \"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel-international\/topic-1-formulae-equations-and-amount-of-substance\/empirical-and-molecular-formulae\/\",\n            \"name\": \"Empirical and Molecular Formulae Revision Notes\",\n            \"description\": \"A Level Chemistry landing page for empirical and molecular formulae, including empirical formulae calculations and molecular formulae calculations.\",\n            \"inLanguage\": \"en-GB\",\n            \"isPartOf\": {\n              \"@type\": \"WebSite\",\n              \"@id\": \"https:\/\/www.onlinelearningsystem.net\/xyz\/#website\",\n              \"name\": \"Online Learning System\",\n              \"url\": \"https:\/\/www.onlinelearningsystem.net\/xyz\/\"\n            },\n            \"about\": [\n              {\n                \"@type\": \"Thing\",\n                \"name\": \"Empirical formulae\"\n              },\n              {\n                \"@type\": \"Thing\",\n                \"name\": \"Molecular formulae\"\n              },\n              {\n                \"@type\": \"Thing\",\n                \"name\": \"Mole ratios\"\n              },\n              {\n                \"@type\": \"Thing\",\n                \"name\": \"Relative molecular mass\"\n              }\n            ],\n            \"author\": {\n              \"@type\": \"Person\",\n              \"name\": \"Dr. Mohammed Al-Fatah\",\n              \"url\": \"https:\/\/www.linkedin.com\/in\/doctormohammedfatah\/\"\n            },\n            \"publisher\": {\n              \"@type\": \"Organization\",\n              \"name\": \"Online Learning System\",\n              \"url\": \"https:\/\/www.onlinelearningsystem.net\/xyz\/\"\n            }\n          },\n          {\n            \"@type\": \"BreadcrumbList\",\n            \"@id\": \"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel-international\/topic-1-formulae-equations-and-amount-of-substance\/empirical-and-molecular-formulae\/#breadcrumb\",\n            \"itemListElement\": [\n              {\n                \"@type\": \"ListItem\",\n                \"position\": 1,\n                \"name\": \"Revision Notes\",\n                \"item\": \"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/\"\n              },\n              {\n                \"@type\": \"ListItem\",\n                \"position\": 2,\n                \"name\": \"A Level Chemistry\",\n                \"item\": \"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/\"\n              },\n              {\n                \"@type\": \"ListItem\",\n                \"position\": 3,\n                \"name\": \"Edexcel International\",\n                \"item\": \"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel-international\/\"\n              },\n              {\n                \"@type\": \"ListItem\",\n                \"position\": 4,\n                \"name\": \"Topic 1 Formulae, Equations and Amount of Substance\",\n                \"item\": \"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel-international\/topic-1-formulae-equations-and-amount-of-substance\/\"\n              },\n              {\n                \"@type\": \"ListItem\",\n                \"position\": 5,\n                \"name\": \"Empirical and Molecular Formulae\",\n                \"item\": \"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel-international\/topic-1-formulae-equations-and-amount-of-substance\/empirical-and-molecular-formulae\/\"\n              }\n            ]\n          }\n        ]\n      }\n      <\/script>\n    <\/main>\n<\/section>\n","protected":false},"excerpt":{"rendered":"<p>Revision Notes \/ A Level Chemistry \/ Edexcel International \/ Topic 1 Formulae, Equations and Amount of Substance \/ Empirical and Molecular Formulae Empirical and Molecular Formulae Use this landing page to move quickly between the key empirical and molecular formulae revision pages for Topic 1. 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