Question

The mass numbers of two elements $X$ and $Z$ are $52$ and $75$ respectively. $X$ contains $16.6 \%$ more neutrons compared to protons. $Z$ contains $27.3 \%$ more neutrons compared to protons. $X$ and $Z$ are respectively

• A. ${ }_{24} Cr _{\text {, } 33}As$
• B. ${ }_{24} Cr _{\text {' } 30} Zn$
• C. ${ }_{19} K _{133} As$
• D. $_{29} Cu _{130} Zn$

Answer 1

Answer: (A)

Given, mass number of $X=52$

Mass number of $Z=75$

Suppose, number of protons in $X=a$

$\therefore $ Number of neutrons $=0.166\, a+a=1.166\, a$

As we know that,

Mass number $=$ Number of proton $+$ Number of neutron

$\therefore 52=a+1.166 \,a$

$52=2.166 \,a$

$a=24$

Thus, the element $X={ }_{24} Cr$

$[\because$ atomic number $=$ number of protons or electrons]

Similarity, for the element $Z$,

$75=b+1.273\, b=2.273\, b$

$b=32.9 \approx 33$

Thus, the element $Z$ is ${ }_{33}\, As$.