What is the general formula of alkenes?

The molecules of alkene family are represented by a general formula ${\mathrm{C}}_{\mathrm{n}}{\mathrm{H}}_{2\mathrm{n}}$. What do $\mathrm{n}$ and $2\mathrm{n}$ signify?

The molecules of alkene family are represented by a general formula ${\mathrm{C}}_{\mathrm{n}}{\mathrm{H}}_{2\mathrm{n}}$. What is the lowest value which can be assigned to $\mathrm{n}$?

The molecules of alkene family are represented by a general formula ${\mathrm{C}}_{\mathrm{n}}{\mathrm{H}}_{2\mathrm{n}}$. What is the molecular formula of alkene when $\mathrm{n}=4$?

The molecule of alkenes family are represented by a general formula ${\mathrm{C}}_{\mathrm{n}}{\mathrm{H}}_{2\mathrm{n}}$. What is a molecular formula of the alkene if there are eight $\mathrm{H}$ atoms in it?

The molecule of alkene family are represented by a general formula ${\mathrm{C}}_{\mathrm{n}}{\mathrm{H}}_{2\mathrm{n}}$. What is the molecular formula of the first member of the alkene family?

The molecule of alkene family are represented by a general formula ${\mathrm{C}}_{\mathrm{n}}{\mathrm{H}}_{2\mathrm{n}}$. What is the molecular formula of the adjacent lower and higher homologues of an alkene which contains four carbon atoms.