# Question-

The solution is as follows:

Since we have been told to find the total Mg

^{2}

^{+}concentration in the solution and not the one which is in equilibrium with MgF

_{2}, it will be the total concentration of Mg

^{2}

^{+}in the solution, which is:

$Totalvolume=10+25=35ml\phantom{\rule{0ex}{0ex}}Given:Initial\left[M{g}^{2+}\right]=0.25M,Initialvolume=10ml\phantom{\rule{0ex}{0ex}}Initial\left[{F}^{-}\right]=0.2M,initialvolume=35ml\phantom{\rule{0ex}{0ex}}\phantom{\rule{0ex}{0ex}}\left[M{g}^{2+}\right]=\frac{10ml}{35ml}\times 0.25M=7.14\times {10}^{-2}M\phantom{\rule{0ex}{0ex}}\left[{F}^{-}\right]=\frac{25ml}{35ml}x0.2M=14x{10}^{-2}M\phantom{\rule{0ex}{0ex}}\phantom{\rule{0ex}{0ex}}\phantom{\rule{0ex}{0ex}}$

Thus, the correct answer is option (b).

Hope it helps.

Regards

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