$T _{ r +1} ={ }^{ n } C _{ r }( x )^{ n – r }\left(\frac{ a }{ x ^{2}}\right)^{ r }$

$={ }^{n} C _{ r } a ^{ r } x ^{ n -3 r }$

${ }^{ n } C _{2} a ^{2}:{ }^{ n } C _{3} a ^{3}:{ }^{ n } C _{4} a ^{4}=12: 8: 3$

After solving

$n =6, a =\frac{1}{2}$

For term independent of $x ^{\prime} \Rightarrow n =3 r$

$r =2$

$\therefore$ Coefficient is ${ }^{6} C _{2}\left(\frac{1}{2}\right)^{2}=\frac{15}{4}$

Nearest integer is $4 .$