Hello,

The reaction is taking place between Mg(NO3)2 and NaOH

Mg(NO3)2 + 2NaOH Mg(OH)2 + 2(NaNO3)

Since, NaNO3 is soluble in water, it will be in aqueous state in above reaction. So, the only solid material in the product side will be Mg(OH)2

We know that,

[ OH -] = √  Ksp / m ( Mg(OH)2)......... ( where, m is Molarity )

So, [ OH - ] = √  ( 5.61 x 10^-12 ) / 0.1

Hence, [ OH - ] = 7.5 x 10^-6 M

Now, pOH = -log [ OH - ]

So, pOH = 5.2

Also, We know that,

pH + pOH = 14

Hence, pH = 14 - 5.2

So, pH = 8.8

Hence, the pH value is 8.8

Best Wishes.