How much water should be added to $200 \, cc$ of a semi-normal solution of $NaOH$ to make it exactly deci-normal?

The molarity of $0.006 \ mol$ of $NaCl$ in $100 \ mL$ solution is (in $M$)

Calculate the mass fraction and mass percentage of aspirin in a solution prepared by dissolving $3.65 \, g$ of aspirin in $25.08 \, g$ of water.

The density of a $2.05 \ M$ solution of acetic acid $(CH_3COOH)$ in water is $1.02 \ g \ mL^{-1}$. The molality of the solution is ......... $mol \ kg^{-1}$.

$300 \ g$ of $25\%$ solution and $400 \ g$ of $40\%$ solution are mixed by weight. Calculate the percentage of the solute by weight in the final mixture. (in $\%$)

If $80 \ g$ of copper sulphate $CuSO_{4} \cdot 5H_{2}O$ is dissolved in deionised water to make $5 \ L$ of solution. The concentration of the copper sulphate solution is $x \times 10^{-3} \ mol \ L^{-1}$. The value of $x$ is .... .
[Atomic masses: $Cu = 63.54 \ u, S = 32 \ u, O = 16 \ u, H = 1 \ u$]