The number of neutrons are equal to the number of protons present in the nucleus of two elements and their respective dinegative ions possess 8 electrons in L and M shells respectively . Then the ratio of mass numbers of the two elements is

Options

A. 1:2
B. 2:3
C. 3:4
D. 2:5

Answer

a

Explanation

The electronic configuration of the dinegative ion with 8 in electrons in the L valence shell is:
`X^(-2) to 2, 8`
`X to 2, 6 (Z)`, mass number is 16 for X.
The electronic configuration of the dinegative ion with 8 electrons in the M shell is
`Y^(-2) to 2,8, 8`
`Y to 2, 8, 6 (Z)`
Mass number is 32 (A) for Y.
Ratio of massnumber is `16 : 32rArr 1 : 2`