The average molecular weight of the air which has $21 \%$ of $\mathrm{O}_2$ and $79 \%$ of $\mathrm{N}_2$, is

The number of significant figures in 2.0400 is

Identify the values of $a, b, c, d$ and $e$ for the following unbalanced reaction,

$$ \begin{aligned} a \mathrm{KNO}_3+5 \mathrm{C}_{12} \mathrm{H}_{22} \mathrm{O}_{11} \longrightarrow b \mathrm{~N}_2 & +c \mathrm{CO}_2 +d \mathrm{H}_2 \mathrm{O}+e \mathrm{~K}_2 \mathrm{CO}_3 \end{aligned} $$

Given,

$$ \mathrm{H}_2(g)+\frac{1}{2} \mathrm{O}_2(g) \longrightarrow \mathrm{H}_2 \mathrm{O}(l) ; \Delta H=-285 \mathrm{~kJ} $$

$$ \begin{aligned} & \mathrm{N}_2 \mathrm{O}_5(g)+\mathrm{H}_2 \mathrm{O}(l) \longrightarrow 2 \mathrm{HNO}_3(l) ; \Delta H=-76.6 \mathrm{~kJ} \\ & \mathrm{~N}_2(g)+3 \mathrm{O}_2(g)+\mathrm{H}_2(g) \longrightarrow 2 \mathrm{HNO}_3(l) ; \\ & \Delta H=-348.2 \mathrm{~kJ} \end{aligned} $$

Calculate the $\Delta \mathrm{H}$ of $2 \mathrm{~N}_2(\mathrm{~g})+5 \mathrm{O}_2(\mathrm{~g}) \longrightarrow 2 \mathrm{~N}_2 \mathrm{O}_5(\mathrm{~g})$.