Consider the following sequence of reactions.

Total number of $$sp^{3}$$ hybridised carbon atoms in the major product C formed is________

The given sequence involves two standard transformations:
(i) $$\text{alkyl halide} \xrightarrow{KCN,\;\text{alc.},\;\Delta} \text{nitrile}$$ (nucleophilic substitution)
(ii) $$\text{nitrile} \xrightarrow{LiAlH_4/\;\text{ether}} \text{primary amine}$$ (complete reduction)

Step-1 (Substitution):
Starting alkyl halide $$A$$ is $$\left(CH_3\right)_2CHBr$$ (2-bromopropane).
Treatment with alcoholic $$KCN$$ gives the nitrile $$B$$ by $$\mathrm{S_N2}$$ substitution:

$$\left(CH_3\right)_2CHBr \;+\; KCN \;\longrightarrow\; \left(CH_3\right)_2CHCN \;+\; KBr$$

Step-2 (Reduction):
The nitrile $$B$$ is reduced with $$LiAlH_4$$ to a primary amine $$C$$:

$$\left(CH_3\right)_2CHCN \;\xrightarrow{LiAlH_4/\text{ether}}\; \left(CH_3\right)_2CHCH_2NH_2$$

Thus the major product $$C$$ is isobutylamine.

Counting $$sp^3$$ hybridised carbons in $$C$$:
• Two methyl carbons: $$2$$
• One secondary carbon (attached to two methyls and $$CH_2$$): $$1$$
• One methylene carbon attached to $$NH_2$$: $$1$$

Total $$sp^{3}$$ hybridised carbon atoms $$= 2 + 1 + 1 = 4$$

Therefore, the required number is 4.