Which of the following statement(s) is/are correct regarding $\mathrm{Ni}(\mathrm{CO}{)}_4$ ?

(P) It has tetrahedral geometry.

(Q) It is diamagnetic in nature. 

(R) It has all Ni-C bonds of equal length.

The electronic configuration of Ni in  $\left[\mathrm{Ni}(\mathrm{CO}{)}_4\right]$ is $3{\mathrm{d}}^{10}4{\mathrm{s}}^0$. Since it forms four coordinate bonds with CO, its hybridization is  ${\mathrm{sp}}^3$, and Ni is diamagnetic because all of its electrons are paired.

Hence, option D is correct.