For an octahedral complex $MX_{4}Y_{2}$ ($M=$ a transition metal,$X$ and $Y$ are monodentate achiral ligands),the correct statement among the following is

• A
  $MX_{4}Y_{2}$ has $2$ geometrical isomers,one of which is chiral
• B
  $MX_{4}Y_{2}$ has $2$ geometrical isomers both of which are achiral
• C
  $MX_{4}Y_{2}$ has $4$ geometrical isomers,all of which are achiral
• D
  $MX_{4}Y_{2}$ has $4$ geometrical isomers,two of which are chiral