Which compound is soluble in $NH_4OH$?

$\cos ^{-1}\left(\frac{-1}{2}\right)-2 \sin ^{-1}\left(\frac{1}{2}\right)+3 \cos ^{-1}\left(\frac{-1}{\sqrt{2}}\right)-4 \tan ^{-1}(-1)$ equals:

$A$ thin semi-circular ring of radius $r$ has a positive charge $q$ distributed uniformly over it. The net electric field $\vec{E}$ at the center $O$ is:

How many litres of oxygen (at $STP$) are required for complete combustion of $39 \text{ g}$ of liquid benzene? (Atomic weights: $C=12, O=16, H=1$)

Which of the following metals forms a saline hydride?

The least value of the natural number $n$ satisfying $C(n, 5) + C(n, 6) > C(n+1, 5)$ is