Chapter 12A.3, Problem 9P

The base peak in the mass spectrum of 2, 2, 4-trimethylpentane $\left[{\left({\text{CH}}_{\text{3}}\right)}_{\text{3}}{\text{CCH}}_{\text{2}}\text{CH}{\left({\text{CH}}_{\text{3}}\right)}_{\text{2}}\right]$

occurs at $m/z=57$ . What ion is responsible for this peak and why is this ion the most

abundant fragment?