The maximum number of unpaired electrons is present in

• Fe

• Cu

• Co

• Ni

The pair, that is referred as 'chemical twins' is

• Ac, Cf

• Hf, Ta

• Tc, Re

• La, Ac

Ce⁴⁺ is stable. This is because of

• half-filled d-orbitals

• all paired electrons ind-orbitals

• empty orbital

• fully filled d-orbital

What is the orbital angular momentum of an electron in 'f'  orbital?

• $\frac{1.5\mathrm{h}}{\mathrm{\pi }}$

• $\frac{\sqrt{6}\mathrm{h}}{\mathrm{\pi }}$

• $\frac{\sqrt{3}\mathrm{h}}{\mathrm{\pi }}$

• $\frac{\sqrt{3}\mathrm{h}}{2\mathrm{\pi }}$

Fool's gold is

• Cu₂S

• FeS₂

• Al₂O₅

• CuFeS₂

Identify a metalloid from the following list of elements.

• Carbon

• Neon

• Sodium

• Tellurium

Identify the weakest oxidising agent among the following.

• Li⁺

• Na⁺

• Cd⁺

• I₂

228.

Which of the following statement(s) is/are incorrect for pair of elements Zr-Hf?

• Both possess same number of valence electrons

• Both have identical sizes

• Both have almost identical radii

• Both of these belong to same period of periodic table

Which element among the following does not form diatomic molecules?

• Argon

• Oxygen

• Nitrogen

• Bromine

Which of the following is covalent?

• NaCl

• KCl

• BeCl

• MgCl₂