The strongest acid among the following is:

The angle of elevation of a stationary cloud from a point $2500 \ m$ above a lake is $15^{\circ}$ and from the same point the angle of depression of its reflection in the lake is $45^{\circ}$. The height (in metres) of the cloud above the lake,given that $\cot 15^{\circ}=2+\sqrt{3}$,is

In $DNA$,the complementary bases are

$\int_{-\pi / 2}^{\pi / 2} \sin |x| \, dx$ is equal to

In an experiment with a beam balance,an unknown mass $m$ is balanced by two known masses of $16 \, kg$ and $4 \, kg$ as shown in the figure. The value of the unknown mass $m$ is ....... $kg$.

If $z = \frac{y}{x} \left[ \sin \frac{x}{y} + \cos \left( 1 + \frac{y}{x} \right) \right]$,then $x \frac{\partial z}{\partial x}$ is equal to