Shown below are the mass spectra $($without data tables$)$ of four molecules. $($The structure of each molecule is shown on the spectrum.$)$

a$.$ Mark the $[M{]}^{+}$peak for each, and indicate the molecular weight of the molecule.

$\frac{m}{z}$

$40$

$q,$

b$.$ Based on the five mass spectra you have seen, describe how one might identify the $[M{]}^{+}$ peak $($molecular ion peak$)$ on the mass spectrum of an unknown compound.