What is the representation of an element having mass number of 40 and 21 neutrons in it?

How many moles of dioxygen are present in $8.314 \times 10^{-3} \mathrm{~m}^3$ of it at 318 K having pressure $3.18 \times 10^5 \mathrm{Nm}^{-2} ?\left(\mathrm{R}=8.314 \mathrm{~J} \mathrm{~K}^{-1} \mathrm{~mol}^{-1}\right)$

Which of the following compounds has difficulty in breaking the $\mathrm{C}-\mathrm{Cl}$ bond?

Identify the alkene obtained as major product in the following Hofmann elimination reaction. $$ \left(\mathrm{C}_3 \mathrm{H}_7\right) \mathrm{N}^{\ominus}\left(\mathrm{C}_2 \mathrm{H}_5\right)_3 \mathrm{I}^{\ominus} \xrightarrow[\Delta]{\text { mois } \mathrm{A}_2 \mathrm{O}} \mathrm{~A} \xrightarrow[\text { Alkene }+\mathrm{H}]{\stackrel{-\mathrm{H}_2 \mathrm{O}}{ }} $$ $\mathrm{Alkene + Amine}$