A hydrocarbon contains $85.7 \%C$ If $42\;mg$ of the compound contains $3.01 \times 10^{20}$ molecules, the molecular formula of the compound is

Question

$(a)\;C_6 H_{14} \\ (b)\;C_6H_{10} \\(c)\;C_6H_6 \\(d)\;C_6H_{12}$