Which of the following has the highest mass?

Suppose you have to determine the percentage of carbon dioxide in a sample of a gas available in a container. Which is the best absorbing material for the carbon dioxide?

When $100 \ mL$ of $1 \ M \ NaOH$ solution and $10 \ mL$ of $10 \ N \ H_2SO_4$ solution are mixed together,the resulting solution will be

When metallic copper comes in contact with moisture,a green powdery/pasty coating can be seen over it. This is chemically known as

Rearrange the following ($I$ to $IV$) in the order of increasing masses:
$(I)$ $0.5$ mole of $O_3$
$(II)$ $0.5 \, g$ atom of oxygen
$(III)$ $3.011 \times 10^{23}$ molecules of $O_2$
$(IV)$ $5.6 \, L$ of $CO_2$ at $STP$

An aqueous solution of $6.3 \ g$ oxalic acid dihydrate is made up to $250 \ mL$. The volume of $0.1 \ N \ NaOH$ required to completely neutralize $10 \ mL$ of this solution is $...... \ mL$.