Which one of the following pairs of terms/names mean one and the same thing?

The oxidation number of $C$ in $HNC$ is .......

The solution of the differential equation $(3xy + y^2)dx + (x^2 + xy)dy = 0$ is

$A$ nucleus $_Z{X^A}$ emits an $\alpha$-particle with velocity $v$. The recoil speed of the daughter nucleus is

If the distance between the centres of the Earth and the Moon is $D$ and the mass of the Earth is $81$ times the mass of the Moon,then at what distance from the centre of the Earth will the net gravitational field be zero?

Which was the first inorganic pesticide developed on a commercial scale?