What is the percentage by mass of oxygen in $NaOH$? (Atomic mass of $Na=23 \ u, O=16 \ u, H=1 \ u$)

Calculate the mass percentage of different elements present in sodium sulfate $(Na_2SO_4)$.

In an organic compound,the weight ratio of $C$,$H$,and $N$ atoms is $9 : 1 : 3.5$. If the molecular weight of the compound is $108$,what is its molecular formula?

The empirical formula of a compound is $CH_{2}O$. $0.0835 \ mol$ of the compound contains $1.0 \ g$ of hydrogen. What is the molecular formula of the compound?

Which of the following has the highest percentage of hydrogen?

An organic compound contains carbon,hydrogen,and oxygen with percentages of $38.71\%$,$9.67\%$,and $51.62\%$ respectively. Determine the empirical formula of this compound.