What quantity (in $mL$) of a $45\%$ acid solution of a mono-protic strong acid must be mixed with a $20\%$ solution of the same acid to produce $800 \ mL$ of a $29.875\%$ acid solution?

If $10^{21}$ molecules are removed from $100 \, mg$ of $CO_2$,how many moles of $CO_2$ remain?

Partially dried soil contains $50 \%$ silica and $7 \%$ water. If the original soil contained $12 \%$ water,then the percentage of silica in the original soil is .............. $\%$.

$100 \ mL$,$1 \ M$ $H_2SO_4$ solution of density $1.5 \ g/mL$ is mixed with $400 \ mL$ of water,resulting in a diluted solution of density $1.25 \ g/mL$. Find the molarity of the final diluted solution. (Density of water $= 1 \ g/mL$)

State whether the following statements are true or false:
$(i)$ $^\circ F = \frac{9}{5} (^\circ C) + 32$
$(ii)$ In $1808$,Dalton published the law of chemical combination in the journal "New System of Chemical Philosophy".
$(iii)$ If the molar mass of a dibasic acid is $100$,its equivalent mass is $200$.

Mohr's salt is