In the crystal of $CuSO_4 \cdot 5H_2O$,the copper atom is coordinated by:

Which complex has a square planar structure?

Which one of the following is an inner orbital complex as well as diamagnetic in behaviour? (Atomic number: $Zn = 30$,$Cr = 24$,$Co = 27$,$Ni = 28$)

In which of the following complex ions is the value of the magnetic moment (spin only) $\sqrt{3} \ B.M.$ and outer $d-$orbitals are used in hybridization?

An octahedral complex of $Ni(II)$ must be:

Which of the following sequences of hybridisation, geometry, and magnetic nature are correct for the given coordination compounds?
$A.$ $[NiCl_4]^{2-}$ – $sp^3$, tetrahedral, paramagnetic  
$B.$ $[Ni(NH_3)_6]^{2+}$ – $sp^3d^2$, octahedral, paramagnetic  
$C.$ $[Ni(CO)_4]$ – $sp^3$, tetrahedral, paramagnetic  
$D.$ $[Ni(CN)_4]^{2-}$ – $dsp^2$, square planar, diamagnetic  
Choose the correct answer from the options given below: