The correct option(s) regarding the complex ${\left[Co\left(en\right){\left(N{H}_3\right)}_3\left(H_{2}O\right)\right]}^{3+}$ :-
(en $= H_{2}NC{H}_{2}C{H}_{2}N{H}_2$ ) is (are)

• Correct answer
  A

  It has two geometrical isomers
• Correct answer
  B

  It will have three geometrical isomers if bidentate 'en' is replaced by two cyanide ligands
• C

  It is paramagnetic
• Correct answer
  D

  It absorbs light at longer wavelength as compared to ${\left[Co\left(en\right){\left(N{H}_3\right)}_4\right]}^{3+}$

Solution

$\left(i\right)$ ${\left[Co\left(en\right){\left(N{H}_3\right)}_3\left(H_{2}O\right)\right]}^{+3}$ complex is type of $\left[M\left(AA\right)b_{3}c\right]$ have two G.I.

$\left(B\right)$ If (en) is replaced by two cyanide ligand, complex will be type of $\left[M{a}_3{b}_{2}c\right]$ and have 3 G.I.

$\left(iii\right)$ ${\left[Co\left(en\right){\left(N{H}_3\right)}_3\left(H_{2}O\right)\right]}^{3+} have d^6 configuration \left(t_{62g}^6\right)$ on central metal with SFL therefore it is dimagnetic in nature.
$\left(iv\right)$ Complex ${\left[Co\left(en\right){\left(N{H}_3\right)}_3\left(H_{2}O\right)\right]}^{3+}$ have lesser $CFSE \left({∆}_O\right)$ value than ${\left[Co\left(en\right){\left(N{H}_3\right)}_4\right]}^{3+}$ therefore complex ${\left[Co\left(en\right){\left(N{H}_3\right)}_3\left(H_{2}O\right)\right]}^{+}$ absorbs longer wavelength for d-d transition

Hence, the correct answer is options: 'A', 'B', 'D'.