The molecular formula of diphenylmethane is $C_{13}H_{12}$. How many structural isomers are possible when one hydrogen atom is replaced by a chlorine atom?

The number of common tangents to the circles ${x^2 + y^2 - 4x - 6y - 12 = 0}$ and ${x^2 + y^2 + 6x + 18y + 26 = 0}$ is

Which one of the following is mainly responsible for the depletion of the ozone layer?

For a binomial variate $X$ with parameters $n=5$ and $p=\frac{3}{4}$,if $\alpha=\frac{1}{9} P(X \geq 3)$ and $\beta=P(X \leq 2)$,then $256(\beta-\alpha)=$

$A$ mass $M$,attached to a horizontal spring,executes $S.H.M.$ with amplitude $A_1$. When the mass $M$ passes through its mean position,a smaller mass $m$ is placed over it and both of them move together with amplitude $A_2$. The ratio of $\left( \frac{A_1}{A_2} \right)$ is

If $\frac{1}{2} \leq x \leq 1$,then $\cos ^{-1} x+\cos ^{-1}\left(\frac{x}{2}+\frac{1}{2} \sqrt{3-3 x^2}\right)$ is equal to