What is the mole fraction of the solute in a $1.00 \, m$ aqueous solution?

The molarity of a solution obtained by mixing $750 \, mL$ of $0.5 \, M \, HCl$ with $250 \, mL$ of $2 \, M \, HCl$ will be $......... \, M$.

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

The unit of mole fraction is:

If $5.85 \ g$ of $NaCl$ is dissolved in $72 \ g$ of water,find the mole fraction of $NaCl$.

Given below are two statements: one is labelled as Assertion $A$ and the other is labelled as Reason $R$.
Assertion $A$: At $10^{\circ} C$,the density of a $5 \ M$ solution of $KCl$ is given. The solution is cooled to $-21^{\circ} C$. The molality of the solution will remain unchanged.
Reason $R$: The molality of a solution does not change with temperature as mass remains unaffected by temperature.
In the light of the above statements,choose the correct answer from the options given below: