The number of unit cells in $58.5 \ g$ of $NaCl$ is nearly

If the equilibrium constant for the reaction,$H_{2(g)} + I_{2(g)} \rightleftharpoons 2 HI_{(g)}$ is $K$,what is the equilibrium constant of $HI_{(g)} \rightleftharpoons \frac{1}{2} H_{2(g)} + \frac{1}{2} I_{2(g)}$?

$A$ lens of power $+2 \text{ diopters}$ is placed in contact with a lens of power $-1 \text{ diopter}$. The combination will behave like:

Two springs have spring constants $K_A$ and $K_B$ such that $K_A > K_B$. If both springs are stretched by the same extension $x$,the work required will be:

Who proposed the theory that "Cells arise only from the pre-existing cells"?

If $\sin ^{-1}\left(\frac{3}{x}\right)+\sin ^{-1}\left(\frac{4}{x}\right)=\frac{\pi}{2}$,then $x$ is equal to