Which of the following ions is paramagnetic?

Which block element from the following are known as transition elements?

The aqueous solution containing which one of the following ions will be colourless?

Which of the following ions will exhibit colour in aqueous solution?

Assertion $(A)$: While going from left to right in the periodic table,the atomic size decreases more rapidly for the $3d$-series compared to the $4f$-series of elements.
Reason $(R)$: $3d$-electrons experience lesser shielding than $4f$-electrons.

Write a brief note on the electronic configurations of the transition elements.