Which of the following element does not show allotropy?

Choose the incorrect statements regarding the central$\mathrm{O}$-atom in ${\mathrm{Cl}}_2{\mathrm{O}}_7,{\mathrm{N}}_2{\mathrm{O}}_5$ and ${\mathrm{HNO}}_3$

a. In each compound the central $\mathrm{O}$-atom is ${\mathrm{sp}}^3$ hybridized with two lone pairs.

b. In each compound, bond angle is greater than $109°$${28}^{\text{'}}$ around central $\mathrm{O}-$atom due to $\mathrm{lp}-\mathrm{lp}$repulsion.

c. Bond angle is less than$109°{28}^{\text{'}}$ around central oxygen atom only in ${\mathrm{HNO}}_3$.

d. In ${\mathrm{Cl}}_2{\mathrm{O}}_7,$ bond angle around central $\mathrm{O}-$atom is nearly $120°$ because $\mathrm{O}-$atom is ${\mathrm{sp}}^2$ hybridized.

Which of the following is a correct match?

a. ${\mathrm{H}}_2\mathrm{O}>{\mathrm{H}}_2\mathrm{S}>{\mathrm{H}}_2\mathrm{Se}>{\mathrm{H}}_2\mathrm{Te}:$ Thermal stability

b. $\mathrm{He}<\mathrm{Ne}<\mathrm{Ar}<\mathrm{Kr}<\mathrm{Xe}:$ Ease of liquefaction

c. $\mathrm{HF} >\mathrm{HI} >\mathrm{HBr} >\mathrm{HCl}:$ Order of boiling point

d. ${\mathrm{H}}_2\mathrm{O}<{\mathrm{H}}_2\mathrm{S}<{\mathrm{H}}_2\mathrm{Se}<{\mathrm{H}}_2\mathrm{Te}:$ Reducing character