Given that:
$a/b=1/3,b/c=2,c/d=1/2,d/e=3,e/f=1/4$
Now calculate;
$\frac{a}{d}=(a/b)*(b/c)*(c/d)\implies(1/3)*(2)*(1/2)=1/3$
$\frac{b}{e}=(b/c)*(c/d)*(d/e)\implies (2)*(1/2)*(3)=3$
$\frac{c}{f}=(c/d)*(d/e)*(e/f)=(1/2)*(3)*(1/4)=3/8$
so $\frac{abc}{def}=(1/3)*(3)*(3/8)=\frac{3}{8}$
Option (A) is correct.