Question
Among the following, the optically inactive compound is

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| Element | Atomic mass |
| $A$ | $12.01$ |
| $B$ | $35.5$ |
$A$ and $B$ combine to form new substance $X$ . If $4\,moles$ of $B$ combine with $1\,mole$ of $A$ to give $1\,mole$ of $X,$ then weight of one mole of $X$ is ........... $\mathrm{g}$

Assertion $A$ : The first ionization enthalpy for oxygen is lower than that of nitrogen.
Reason $R$ : The four electrons in $2 p$ orbitals of oxygen experience more electron-electron repulsion.
In the light of the above statements, choose the correct answer from the options given below.