What is the value of percent atom economy when reactants having a sum of formula weight $78 \ u$ result in the formation of a product with a formula weight of $65 \ u$ (in $\%$)?

Sodium oxide reacts with water to produce sodium hydroxide. $20.0 \ g$ of sodium oxide is dissolved in $500 \ mL$ of water. Neglecting the change in volume,the concentration of the resulting $NaOH$ solution is $........ \times 10^{-1} \ M.$ (Nearest integer)
[Atomic mass $: Na=23.0, O=16.0, H=1.0]$

$5 \, M$ solution of $H_2SO_4$ is diluted from $1 \, L$ to $10 \, L$. What is the normality of the solution in $N$?

To neutralize $10 \, mL$ of $M/5$ $NaOH$,the volume of $M/20$ $HCl$ required is......$mL$.

If Avogadro's number is $A_0$,the number of sulphur atoms present in $200 \, mL$ of $1 \, N \, H_2SO_4$ is

What is the weight of oxygen that is required for the complete combustion of $2.8 \ kg$ of ethylene? (in $kg$)