{"id":84637,"date":"2025-06-01T02:42:19","date_gmt":"2025-06-01T02:42:19","guid":{"rendered":"https:\/\/exam.pscnotes.com\/mcq\/?p=84637"},"modified":"2025-06-01T02:42:19","modified_gmt":"2025-06-01T02:42:19","slug":"calcium-atomic-number-20-and-argon-atomic-number-18-have-a-mass-nu","status":"publish","type":"post","link":"https:\/\/exam.pscnotes.com\/mcq\/calcium-atomic-number-20-and-argon-atomic-number-18-have-a-mass-nu\/","title":{"rendered":"Calcium (atomic number 20) and argon (atomic number 18) have a mass nu"},"content":{"rendered":"

Calcium (atomic number 20) and argon (atomic number 18) have a mass number of 40. What are they known as?<\/p>\n

[amp_mcq option1=”Isotones” option2=”Isochores” option3=”Isobars” option4=”Isotopes” correct=”option3″]<\/p>\n

\n
\n
This question was previously asked in<\/div>\n
UPSC CDS-1 – 2017<\/div>\n<\/div>\n
Download PDF<\/a>Attempt Online<\/a><\/div>\n<\/div>\n
\nThe correct answer is C) Isobars.
\n<\/section>\n
\nAtoms of different elements that have the same mass number (sum of protons and neutrons) but different atomic numbers (number of protons) are called isobars. Calcium has atomic number 20 and mass number 40. Argon has atomic number 18 and mass number 40. Since they have different atomic numbers (20 vs 18) but the same mass number (40), they are isobars.
\n<\/section>\n
\n– Isotopes are atoms of the same element (same atomic number) with different mass numbers (different number of neutrons). Example: Carbon-12 and Carbon-14.
\n– Isotones are atoms of different elements (different atomic numbers) with the same number of neutrons. For Calcium-40, neutrons = 40-20 = 20. For Argon-40, neutrons = 40-18 = 22. They are not isotones.
\n– Isochores relate to constant volume processes in thermodynamics, not atomic structure.
\n<\/section>\n","protected":false},"excerpt":{"rendered":"

Calcium (atomic number 20) and argon (atomic number 18) have a mass number of 40. What are they known as? [amp_mcq option1=”Isotones” option2=”Isochores” option3=”Isobars” option4=”Isotopes” correct=”option3″] This question was previously asked in UPSC CDS-1 – 2017 Download PDFAttempt Online The correct answer is C) Isobars. Atoms of different elements that have the same mass number … <\/p>\n

Detailed SolutionCalcium (atomic number 20) and argon (atomic number 18) have a mass nu<\/span><\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[1087],"tags":[1101,1162,1096],"class_list":["post-84637","post","type-post","status-publish","format-standard","hentry","category-upsc-cds-1","tag-1101","tag-atomic-structure","tag-chemistry","no-featured-image-padding"],"yoast_head":"\nCalcium (atomic number 20) and argon (atomic number 18) have a mass nu<\/title>\n<meta name=\"description\" content=\"The correct answer is C) Isobars. Atoms of different elements that have the same mass number (sum of protons and neutrons) but different atomic numbers (number of protons) are called isobars. Calcium has atomic number 20 and mass number 40. Argon has atomic number 18 and mass number 40. Since they have different atomic numbers (20 vs 18) but the same mass number (40), they are isobars.\" \/>\n<meta name=\"robots\" content=\"index, follow, max-snippet:-1, max-image-preview:large, max-video-preview:-1\" \/>\n<link rel=\"canonical\" href=\"https:\/\/exam.pscnotes.com\/mcq\/calcium-atomic-number-20-and-argon-atomic-number-18-have-a-mass-nu\/\" \/>\n<meta property=\"og:locale\" content=\"en_US\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"Calcium (atomic number 20) and argon (atomic number 18) have a mass nu\" \/>\n<meta property=\"og:description\" content=\"The correct answer is C) Isobars. Atoms of different elements that have the same mass number (sum of protons and neutrons) but different atomic numbers (number of protons) are called isobars. Calcium has atomic number 20 and mass number 40. Argon has atomic number 18 and mass number 40. Since they have different atomic numbers (20 vs 18) but the same mass number (40), they are isobars.\" \/>\n<meta property=\"og:url\" content=\"https:\/\/exam.pscnotes.com\/mcq\/calcium-atomic-number-20-and-argon-atomic-number-18-have-a-mass-nu\/\" \/>\n<meta property=\"og:site_name\" content=\"MCQ and Quiz for Exams\" \/>\n<meta property=\"article:published_time\" content=\"2025-06-01T02:42:19+00:00\" \/>\n<meta name=\"author\" content=\"rawan239\" \/>\n<meta name=\"twitter:card\" content=\"summary_large_image\" \/>\n<meta name=\"twitter:label1\" content=\"Written by\" \/>\n\t<meta name=\"twitter:data1\" content=\"rawan239\" \/>\n\t<meta name=\"twitter:label2\" content=\"Est. reading time\" \/>\n\t<meta name=\"twitter:data2\" content=\"1 minute\" \/>\n<!-- \/ Yoast SEO Premium plugin. -->","yoast_head_json":{"title":"Calcium (atomic number 20) and argon (atomic number 18) have a mass nu","description":"The correct answer is C) Isobars. 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Atoms of different elements that have the same mass number (sum of protons and neutrons) but different atomic numbers (number of protons) are called isobars. Calcium has atomic number 20 and mass number 40. Argon has atomic number 18 and mass number 40. 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