The correct option is B CnH2n+2
The general formula of a non-cyclic alkane is CnH2n+2. In unbranched carbon chain, each carbon in the middle of the chain is connected to 2 carbon atoms and 2 hydrogen atoms. The terminal carbon atoms are connected to 3 hydrogen atoms each.
In case of a branched alkane, one of the hydrogens on a carbon is replaced by carbon, but that increases one more terminal carbon which connects to 3 hydrogens. So the general form CnH2n+2 remains the same (except for cycloalkanes).