$\sigma$ orbital has a total of two nodal planes.

$\sigma^{*}$ orbital has one node in the $x z$-plane containing the molecular axis.

$\pi$ orbital has one node in the plane which is perpendicular to the molecular axis and goes through the center of the molecule.

$\pi^{*}$ orbital has one node in the $x y$-plane containing the molecular axis.

Chemisorption results in a unimolecular layer.

The enthalpy change during physisorption is in the range of 100 to $140 \mathrm{~kJ} \mathrm{~mol}^{-1}$.

Chemisorption is an endothermic process.

Lowering the temperature favors physisorption processes.

the reaction of $\mathrm{Al}_{2} \mathrm{O}_{3}$ with coke $(\mathrm{C})$ at a temperature $>2500^{\circ} \mathrm{C}$.

the neutralization of aluminate solution by passing $\mathrm{CO}_{2}$ gas to precipitate hydrated alumina $\left(\mathrm{Al}_{2} \mathrm{O}_{3} \cdot 3 \mathrm{H}_{2} \mathrm{O}\right)$.

the dissolution of $\mathrm{Al}_{2} \mathrm{O}_{3}$ in hot aqueous $\mathrm{NaOH}$.

the electrolysis of $\mathrm{Al}_{2} \mathrm{O}_{3}$ mixed with $\mathrm{Na}_{3} \mathrm{AlF}_{6}$ to give $\mathrm{Al}$ and $\mathrm{CO}_{2}$.

paramagnetic

bent in geometry

an acidic oxide

colorless