Which of the following allotropes of carbon is isomorphous with crystalline silicon?

If $\cos ^{-1}\left(\frac{x^2-y^2}{x^2+y^2}\right)=k$ (a constant),then $\frac{d y}{d x}$ is equal to

$A$ bag contains $6$ white and $4$ black balls. Two balls are drawn at random. The probability that they are of the same colour is:

Assertion $(A)$: Cyclohexane is the most stable cycloalkane.
Reason $(R)$: Cyclopropane and cyclobutane are less stable due to angle strain and torsional strain.
The correct answer is:

The number of subsets of $\{1, 2, 3, \ldots, 9\}$ containing at least one odd number is

If the angular momentum of an electron is $\overrightarrow{J}$,then the magnitude of the magnetic moment will be