Ahydrocarbon consists of four carbon atoms with one double bond. predict the molecular formula of this compound.

These ones it helps to draw. you have four carbons and each one must have 4 covalent bonds coming off of it, but the double bond will act as a 2 covalent bonds between carbon atoms rather than 1. You should get C4H8. Alternatively the alkene formula can be used (alkenes are molecules with a C to C double bond) which states CnH2n will be the Molecular formula where n is the number of carbons.