MCQ
Consider the following statements ( $X$ and $Y$ stand for two different elements):

$(I)$ ${ }_{32}^{65} X$ and ${ }_{33}^{65} Y$ are isotopes.

$(II)$ ${ }_{42}^{86} X$ and ${ }_{42}^{85} Y$ are isotopes.

$(III)$ ${ }_{85}^{174} X$ and ${ }_{88}^{177} Y$ have the same number of neutrons.

$(IV)$ ${ }_{92}^{235} X$ and ${ }_{94}^{235} Y$ are isobars.

Which of the above statements are correct?

  • A
    Only statements $II$ and $IV$ are correct
  • B
    Only statements $I, II$ and $IV$ are correct
  • Only statements $II, III$ and $IV$ are correct
  • D
    All statements are correct

Answer

Correct option: C.
Only statements $II, III$ and $IV$ are correct
c
(c)

For a nucleus, ${ }_Z^A X$

Mass number, $A=N+Z$

where, $N=$ number of neutrons

and $Z=$ number of protons.

In ${ }_{32}^{65} X$ and ${ }_{33}^{65} Y$, number of protons are different. So, these are not isotopes.

In ${ }_{42}^{86} X$ and ${ }_{42}^{85} Y$, number of protons are equal. So, these are isotopes.

In ${ }_{85}^{174} X$ and ${ }_{88}^{177} Y$, number of neutrons are $174-85=89$ and $177-88=89$.

So, both have same number of neutrons.

In ${ }_{92}^{235} X$ and ${ }_{94}^{235} Y$, both have same mass number, so these are isobars.

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