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

$A$ $2 ~kg$ ball moving at $24 ~ms^{-1}$ undergoes an inelastic head-on collision with a $4 ~kg$ ball moving in the opposite direction at $48 ~ms^{-1}$. If the coefficient of restitution is $2/3$,what are their velocities in $ms^{-1}$ after the impact?

Nitrobenzene on reduction with zinc and $NH_4Cl$ gives

This is the only type of pollination which during pollination brings genetically different types of pollen grains to the stigma.

Potato and sweet potato:

$A$ bomb is projected with $200 \, m/s$ at an angle $60^o$ with the horizontal. At the highest point,it explodes into three particles of equal masses. One goes vertically upward with a velocity of $100 \, m/s$,and the second particle goes vertically downward with the same velocity as the first. What is the velocity of the third particle?