What is the atomic number of an element whose $M^{2+}$ ion has the electronic configuration $[Ar] 3d^8$?

If $R$ is an equivalence relation on a set $A$,then $R^{-1}$ is

If $A=35^{\circ}, B=15^{\circ}$ and $C=40^{\circ}$,then $\tan A \cdot \tan B+\tan B \cdot \tan C+\tan C \cdot \tan A$ is equal to

Which type of chromosome is represented by the given figure?

The equation of the line joining the centres of the circles belonging to the coaxial system of circles $4x^2 + 4y^2 - 12x + 6y - 3 + \lambda(x + 2y - 6) = 0$ is

The locus of the poles of focal chords of the parabola $y^2 = 4ax$ is