Question

Four atoms $(A,B,C,D)$ have been grouped in four pairs below. Which one of these pairs forms a pair of isotopes?

• A. ${{}_{7}B}^{14}$ and ${{}_{6}C}^{12}$
• B. ${{}_{6}A}^{14}$ and ${{}_{7}B}^{14}$
• C. ${{}_{6}A}^{14}$ and ${{}_{6}C}^{12}$
• D. ${{}_{6}C}^{12}$ and ${{}_{7}D}^{15}$

Answer 1

The correct option is C ${{}_{6}A}^{14}$ and ${{}_{6}C}^{12}$

Isotopes are atoms with the same number of protons but that have a different number of neutrons. Since the atomic number is equal to the number of protons and the atomic mass is the sum of protons and neutrons, we can also say that isotopes are elements with the same atomic number but different mass numbers. For example, carbon-12, carbon-13 and carbon-14 are three isotopes of the element carbon with mass numbers 12, 13 and 14 respectively but same atomic number 6. So A and C atoms have same atomic number as 6 but different mass numbers 14 and 12.