Both olives and the leaves of olive trees contain alkanes with long carbon chains. A predominant alkane in olives has 27 carbons, whereas a major alkane component in olive leaves has 31 carbons. What is the molecular formula of each of these alkanes?

Explanation:

Alkanes are saturated hydrocarbons (i.e they do not have any double/triple bond within there carbon chain). They have the general formula CₙH₂ₙ₊₂ where n is the number of carbons and starts with 1.

Since the predominant alkane in the olive has 27 carbons, it's molecular formula will be C₂₇H₍₂ₓ₂₇₎₊₂ ⇒ C₂₇H₅₆

The major alkane component in the olive leaves has 31 carbons, hence it's molecular formula will be C₃₁H₍₃₁ₓ₂₎₊₂ ⇒ C₃₁H₆₄

the formula mass of a molecule or a compound is the sum of the atomic weights of the atoms in its empirical formula

(that's what i know about formula mass)