The number of unpaired electrons is maximum in (Atomic no. : $Ti = 22; V = 23; Cr = 24; Fe = 26$)

Which of the following sets of ions contains colored ions?
$(1) \ Cu^{2+}$ $(2) \ Ti^{4+}$ $(3) \ Co^{2+}$ $(4) \ Fe^{3+}$

What is the difference in atomic volume between $Au$ and $Cu$ in $22$ carat gold jewelry?

Which of the following electronic configurations of a metal atom represents the highest oxidation state?

Which elements of the $3d$ series do not show variable valency?

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.