Strength of metallic bond directly depends on the number of unpaired electrons. More is number of unpaired electrons stronger is metallic bond. Hence,metallic bond is strongest in Cr having maximum of 6 unpaired electrons among the given options, i.e., Sc (1 unpaired electron), V (3 unpaired electrons) and Fe (4 unpaired electrons).

Among the given options Ga is the only liquid metal which expands on solidification.It has an unusual structure. Each metal atom has one close neighbour at a distance of 2.43 Å, and six more neighbours at distances within range of 2.70 Å to 2.79 Å. Due to this structure it exists as discrete diatomic molecules rather than a metallic structure in crystal form which is less dense than its liquid form. As its solid form is heated to 30°C,due to weak metallic bonds this unusual structure no longer exists and melts to liquid. This property is unique to Ga, Ge and Bi.

Due to d⁵ configuration, Mn has exactly half filled d-orbitals. As a result the electronic configuration is stable means 3d electrons are more tightly held by the nucleus and this reduces the delocalization of electrons resulting in weaker metallic bonding.

German silver is

Cu = 25 -50%

Zn = 25 -35%

Ni = 10- 35%

Used as utensils, resistance wire.

Configuration of Fe ( Z = 26)

1s², 2s², 2p⁶, 3s², 3p⁶, 3d⁶, 4s²

Cerium (Ce) belongs to lanthanide series and is member of inner-transition metals.

Zirconium (Z = 40).

The ion having all electrons paired is not coloured.

(a) Ti³⁺ = 1s², 2s², 2p⁶, 3s², 3p⁶, 3d¹,4s⁰

(b) Fe³⁺ = 1s², 2s², 2p⁶, 3s², 3p⁶, 3d⁵, 4s⁰

(c) V³⁺ = 1s², 2s², 2p⁶, 3s², 3p⁶, 3d², 4s⁰

(d) Cu+ = 1s², 2s², 2p⁶, 3s², 3p⁶, 3d¹⁰,4s⁰

∵ Only Cu+does not have any unpaired electron, it is not coloured.