When the concentration is expressed as the number of moles of a solute per litre of solution,it is known as:

The density of '$x$' $M$ solution ('$x$' molar) of $NaOH$ is $1.12 \ g \ mL^{-1}$. While in molality,the concentration of the solution is $3 \ m$ $(3 \ molal)$. Then '$x$' is.
(Given: Molar mass of $NaOH$ is $40 \ g \ mol^{-1}$)

$1 \ g$ of a solute is added to $18 \ g$ of water. In this aqueous solution,what is the mass per cent of the solute (in $\%$)?

$4 \ g$ of $NaOH$ is dissolved in $250 \ mL$ of water to prepare a solution. Find the molarity of the solution. (in $M$)

$A$ solution is obtained by mixing $300 \, g$ of $25 \%$ solution and $400 \, g$ of $40 \%$ solution by mass. Calculate the mass percentage of the resulting solution. (in $\%$)

$x$ grams of water is mixed in $69 \ g$ of ethanol. The mole fraction of ethanol in the resultant solution is $0.6$. What is the value of $x$ in grams?