18) D

Let us take an alkane: Butane. Butane is C₄H₁₀

The -NH₂ group will be joined by taking out an hydrogen atom from the butane.

So the formula would be C₄H₁₁N. This amine has one extra hydrogen atom and one nitrogen atom compared to the original butane.

So the general formula would be CnH2n+3n