$0.5 \ L$ of gaseous hydrocarbon when burnt in excess of $O_2$ gave $3.5 \ L$ of $CO_2$ and $4 \ L$ of water vapours under same conditions. The molecular formula of the hydrocarbon will be:

$x \ g$ of methane was burnt completely in the presence of oxygen. The liberated gases were passed into a solution containing $370 \ g$ of $Ca(OH)_2$. The weight of white precipitate obtained was $500 \ g$. What is the value of $x$ (in $g$)? (Given: $C=12, H=1, Ca=40, O=16 \ u$)

To change the strength of $25 \, mL$ of $0.15 \, M$ $HCl$ to $0.1 \, M$,the quantity of water that is to be added is.......$mL$

$A$ $6 \ L$ sample of hard water has a total hardness of $200 \ ppm$ of $Mg^{2+}$ in the form of bicarbonates and chlorides. This sample is treated with $Na_2CO_3$ to eliminate all temporary hardness,and the new hardness is found to be $\frac{1000}{3} \ ppm$ of $CaCO_3$. Find the mass of $MgCl_2$ in the $6 \ L$ sample in $mg$. $(d_{H_2O} = 1 \ g/mL)$

The exact volumes of $1\, M\, NaOH$ solution required to neutralize $50\, mL$ of $1\, M\, H_3PO_3$ solution and $100\, mL$ of $2\, M\, H_3PO_2$ solution,respectively,are:

$1.5 \ mol$ of $O_2$ combine with $Mg$ to form oxide $MgO$. The mass of $Mg$ (atomic mass $24$) that has combined is ............. $g$.