Vivek was given few models of atoms representing their structures. He was asked to choose one pair of isotopes and one pair of isobars.

Which of the following options contains the correct pairs?

Options

A. `{:(" Isotopes","Isobars "),((i) and (ii) ,(iii) and (iv) ):}`
B. `{:(" Isotopes","Isobars "),((i) and (iv), (ii) and (iii) ):}`
C. `{:(" Isotopes","Isobars "),((i) and (iii) ,(ii) and (iv)):}`
D. `{:(" Isotopes","Isobars "),((ii) and (iv), (i) and (iii)):}`

Answer

C

Explanation

Atomic no. = No. of protons Mass no. = No. of protons + No. of neutrons (i) atomic no. = 17 and mass no. = 17 + 18 = 35 (ii) = atomic no. = 18 and mass no. = 18 + 22 = 40 (iii) = atomic no. = 17 and mass no. = 17 + 20 = 37 (iv) atomic no. = 20 and mass no. = 20 + 20 = 40 Out of these four atoms, (i) and (iii) have same atomic no. i.e., 17 but different mass numbers. Hence, they are isotopes. Atoms (ii) and (iv) have same mass no. i.e., 40 but different atomic numbers. Hence, they are isobars.