In order to identify the molecular formula of that compound it would be better if we try to solve for the structure of the compound.
1. 7 octyne means that the triple bond is on the seventh carbon in the 8 carbon chain.
2. 2,4 dimethyl means that there are two (2) methyl (-CH3) groups attached in the 2nd and 4th carbon in the octyne chain.
3. 5 chloro means that the -Cl atom is attached in the 5th carbon in the octyne chain
4. Since it is an alcohol, we can add an -OH in the compound. However, the position of the -OH is not specified.
4. Finally, supply all the remaining bonds with hydrogen (-H) following the octet rule.
We can now get the formula of this compound.