$\underset{\text{3-methylbutanoic acid}}{ CH_{3} - \underset{\overset{|}{CH_{3}}}{CH} - CH_{2}COOH} \ce{->[{NaOH/CaO}][{\Delta}]}$
$CH_{3} -\underset{\overset{|}{\underset{\text{Isobutane}}{CH_{3}}}}{CH} - CH_{3} +CO_{2} \uparrow$
On the other hand Wurtz reaction of $\ce{C2H5Br}$ gives. n-butane and hydrolysis of n-butyl magnesium bromide gives n-butane but reduction of propanol with HI/P gives propane.