{"id":232608,"date":"2025-06-12T04:22:40","date_gmt":"2025-06-12T04:22:40","guid":{"rendered":"https:\/\/learnexams.com\/blog\/?p=232608"},"modified":"2025-06-12T04:22:42","modified_gmt":"2025-06-12T04:22:42","slug":"1s2-2s2-2p6-3s2-3p6-4s2-3d10-4p6-5s1-4d10","status":"publish","type":"post","link":"https:\/\/www.learnexams.com\/blog\/2025\/06\/12\/1s2-2s2-2p6-3s2-3p6-4s2-3d10-4p6-5s1-4d10\/","title":{"rendered":"1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s1 4d10"},"content":{"rendered":"\n

1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s1 4d10 (b) [Kr] 5s2 4d10 5p6 6s1 (c) 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 (d) [Kr] 5s2 4d10 5p6 6s2 4f7<\/p>\n\n\n\n

The Correct Answer and Explanation is:<\/mark><\/strong><\/p>\n\n\n\n

Correct Answer: (b) [Kr] 5s2 4d10 5p6 6s1<\/strong><\/h3>\n\n\n\n
\n\n\n\n

Textbook-Style Explanation:<\/strong><\/h3>\n\n\n\n

To determine the correct electron configuration, we must follow the Aufbau principle<\/strong>, which states that electrons fill atomic orbitals of the lowest available energy levels before occupying higher levels. Additionally, the Pauli exclusion principle<\/strong> and Hund\u2019s rule<\/strong> govern electron distribution within orbitals.<\/p>\n\n\n\n

Option (b) shows the electron configuration:
[Kr] 5s\u00b2 4d\u00b9\u2070 5p\u2076 6s\u00b9<\/strong>
This matches the electron configuration of Cesium (Cs)<\/strong>, which has an atomic number of 55<\/strong>. Cesium has 55 electrons, and this configuration correctly accounts for all of them:<\/p>\n\n\n\n

    \n
  • [Kr] = 36 electrons (up to krypton)<\/li>\n\n\n\n
  • 5s\u00b2 = 2 electrons (36 + 2 = 38)<\/li>\n\n\n\n
  • 4d\u00b9\u2070 = 10 electrons (38 + 10 = 48)<\/li>\n\n\n\n
  • 5p\u2076 = 6 electrons (48 + 6 = 54)<\/li>\n\n\n\n
  • 6s\u00b9 = 1 electron (54 + 1 = 55)<\/li>\n<\/ul>\n\n\n\n

    Thus, this configuration is both correct and complete<\/strong>.<\/p>\n\n\n\n

    Let\u2019s briefly review the other options<\/strong>:<\/p>\n\n\n\n

      \n
    • (a)<\/strong> 1s\u00b2 2s\u00b2 2p\u2076 3s\u00b2 3p\u2076 4s\u00b2 3d\u00b9\u2070 4p\u2076 5s\u00b9 4d\u00b9\u2070
      \u274c Incorrect: The 4d subshell should not be completely filled before the 5p. Also, it gives 48 electrons, which is for Cadmium (Cd)<\/strong>, but the sequence is incorrect.<\/li>\n\n\n\n
    • (c)<\/strong> 1s\u00b2 2s\u00b2 2p\u2076 3s\u00b2 3p\u2076 4s\u00b2 3d\u00b9\u2070 4p\u2076 5s\u00b2
      \u274c Incomplete: This adds up to only 38 electrons, which corresponds to Strontium (Sr)<\/strong>, but lacks noble gas shorthand or higher subshells.<\/li>\n\n\n\n
    • (d)<\/strong> [Kr] 5s\u00b2 4d\u00b9\u2070 5p\u2076 6s\u00b2 4f\u2077
      \u274c Incorrect for any ground-state neutral element. The 4f block starts after 6s and belongs to the lanthanides<\/strong>; 4f\u2077 would be Gadolinium (Gd)<\/strong>, atomic number 64. But the 5d\u00b9 orbital should also be included.<\/li>\n<\/ul>\n\n\n\n

      Therefore, (b)<\/strong> is the only electron configuration that is both correct in order and complete for its element (Cs)<\/strong>.<\/p>\n\n\n\n

      \"\"<\/figure>\n","protected":false},"excerpt":{"rendered":"

      1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s1 4d10 (b) [Kr] 5s2 4d10 5p6 6s1 (c) 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 (d) [Kr] 5s2 4d10 5p6 6s2 4f7 The Correct Answer and Explanation is: Correct Answer: (b) [Kr] 5s2 4d10 5p6 6s1 Textbook-Style Explanation: To determine the correct electron configuration, […]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"site-sidebar-layout":"default","site-content-layout":"","ast-site-content-layout":"default","site-content-style":"default","site-sidebar-style":"default","ast-global-header-display":"","ast-banner-title-visibility":"","ast-main-header-display":"","ast-hfb-above-header-display":"","ast-hfb-below-header-display":"","ast-hfb-mobile-header-display":"","site-post-title":"","ast-breadcrumbs-content":"","ast-featured-img":"","footer-sml-layout":"","ast-disable-related-posts":"","theme-transparent-header-meta":"","adv-header-id-meta":"","stick-header-meta":"","header-above-stick-meta":"","header-main-stick-meta":"","header-below-stick-meta":"","astra-migrate-meta-layouts":"default","ast-page-background-enabled":"default","ast-page-background-meta":{"desktop":{"background-color":"","background-image":"","background-repeat":"repeat","background-position":"center center","background-size":"auto","background-attachment":"scroll","background-type":"","background-media":"","overlay-type":"","overlay-color":"","overlay-opacity":"","overlay-gradient":""},"tablet":{"background-color":"","background-image":"","background-repeat":"repeat","background-position":"center center","background-size":"auto","background-attachment":"scroll","background-type":"","background-media":"","overlay-type":"","overlay-color":"","overlay-opacity":"","overlay-gradient":""},"mobile":{"background-color":"","background-image":"","background-repeat":"repeat","background-position":"center center","background-size":"auto","background-attachment":"scroll","background-type":"","background-media":"","overlay-type":"","overlay-color":"","overlay-opacity":"","overlay-gradient":""}},"ast-content-background-meta":{"desktop":{"background-color":"var(--ast-global-color-5)","background-image":"","background-repeat":"repeat","background-position":"center center","background-size":"auto","background-attachment":"scroll","background-type":"","background-media":"","overlay-type":"","overlay-color":"","overlay-opacity":"","overlay-gradient":""},"tablet":{"background-color":"var(--ast-global-color-5)","background-image":"","background-repeat":"repeat","background-position":"center center","background-size":"auto","background-attachment":"scroll","background-type":"","background-media":"","overlay-type":"","overlay-color":"","overlay-opacity":"","overlay-gradient":""},"mobile":{"background-color":"var(--ast-global-color-5)","background-image":"","background-repeat":"repeat","background-position":"center center","background-size":"auto","background-attachment":"scroll","background-type":"","background-media":"","overlay-type":"","overlay-color":"","overlay-opacity":"","overlay-gradient":""}},"footnotes":""},"categories":[25],"tags":[],"class_list":["post-232608","post","type-post","status-publish","format-standard","hentry","category-exams-certification"],"_links":{"self":[{"href":"https:\/\/www.learnexams.com\/blog\/wp-json\/wp\/v2\/posts\/232608","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.learnexams.com\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.learnexams.com\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.learnexams.com\/blog\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/www.learnexams.com\/blog\/wp-json\/wp\/v2\/comments?post=232608"}],"version-history":[{"count":0,"href":"https:\/\/www.learnexams.com\/blog\/wp-json\/wp\/v2\/posts\/232608\/revisions"}],"wp:attachment":[{"href":"https:\/\/www.learnexams.com\/blog\/wp-json\/wp\/v2\/media?parent=232608"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.learnexams.com\/blog\/wp-json\/wp\/v2\/categories?post=232608"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.learnexams.com\/blog\/wp-json\/wp\/v2\/tags?post=232608"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}