JEE Main 2025 — Some Basic Concepts Of Chemistry Question with Solution

To determine the final concentration of the NaOH solution, we use the formula for mixing solutions :

$M_F=\frac{M_1\times V_1+M_2\times V_2}{V_1+V_2}$

Where :

$M_1=2\text{M}$ and $V_1=20\text{mL}$: Concentration and volume of the first solution.

$M_2=0.5\text{M}$ and $V_2=400\text{mL}$: Concentration and volume of the second solution.

Substitute the values into the equation:

$M_F=\frac{2\times 20+0.5\times 400}{420}$

Calculating each term:

$2\times 20=40$

$0.5\times 400=200$

Add these results:

$M_F=\frac{40+200}{420}=\frac{240}{420}\approx 0.571\text{M}$

Convert this to scientific notation as the problem specifies the answer should be in $\times 10^{-2}$ form:

$M_F=57.1\times 10^{-2}\text{M}$

Rounded to the nearest integer, the final concentration is:

$57$