Identify the major product in the following reaction.

Identify A and B in the given chemical reaction sequence :

Given below are two statements : one is labelled as Assertion (A) and the other is labelled as Reason (R).

Assertion (A) : $$\mathrm{NH}_3$$ and $$\mathrm{NF}_3$$ molecule have pyramidal shape with a lone pair of electrons on nitrogen atom. The resultant dipole moment of $$\mathrm{NH}_3$$ is greater than that of $$\mathrm{NF}_3$$.

Reason (R) : In $$\mathrm{NH}_3$$, the orbital dipole due to lone pair is in the same direction as the resultant dipole moment of the $$\mathrm{N}-\mathrm{H}$$ bonds. $$\mathrm{F}$$ is the most electronegative element.

In the light of the above statements, choose the correct answer from the options given below :

Consider the given chemical reaction :

Product "A" is :