Answer: 0.0725ppm
Explanation:
133.4g of MgBr2 dissolves in 1.84L of water.
Therefore Xg of MgBr2 will dissolve in 1L of water. i.e
Xg of MgBr2 = 133.4/1.84 = 72.5g
The concentration of MgBr2 is 72.5g/L = 0.0725mg/L
Recall,
1mg/L = 1ppm
Therefore, 0.0725mg/L = 0.0725ppm
The pH of the solution is 3,76
Why?
To solve this problem we have to apply the Henderson-Hasselbach equation, which is used whenever we need to calculate the pH of a solution of an acid HA (Lactic Acid) and its conjugate base A⁻ (Sodium Lactate)
We can use either moles or concentrations for this equation. In this case, we are going to use the moles, and we are going to take the pKa of lactic acid as 3,86:

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Here, as they both are physical things without any magnetic property & density difference, screening would be best.
In short, Your Answer would be Option C
Hope this helps!