The $3d-$ metal ions are paramagnetic in nature because

Given below are two statements: one is labelled as Assertion $(A)$ and the other is labelled as Reason $(R)$.
Assertion $(A):$ $Cu^{2+}$ in water is more stable than $Cu^{+}$.
Reason $(R):$ Enthalpy of hydration for $Cu^{2+}$ is much less than that of $Cu^{+}$.
In the light of the above statements,choose the correct answer from the options given below:

Highest density is of $...$.

Write the ground state electronic configurations of $Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu$.

Transition elements form complex compounds due to:

Those elements whose two outermost orbitals are incompletely filled with electrons are known as: