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. ${}_{24}C{r}_{\text{, }33}As$
• B. ${}_{24}C{r}_{\text{’ }30}Zn$
• C. ${}_{19}{K}_{133}As$
• D. ${}_{29}C{u}_{130}Zn$

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 $=0.166a+a=1.166a$

As we know that,

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

$\therefore 52=a+1.166a$

$52=2.166a$

$a=24$

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

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

Similarity, for the element $Z$,

$75=b+1.273b=2.273b$

$b=32.9\approx 33$

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