Understanding of acids and bases
As we are discussing acid-base neutralisation reactions they will be in solution (mixed with water).

First consider LiOH when mixed with water:
$$\ce{LiOH -&gt; Li+ + OH-}$$

As we can see $\ce{OH-}$ ions are formed, meaning this solution is a base.  This means we need an acid to neutralise it.  (Acids and bases react to neutralise each other).

Lets say we use $\ce{HCl}$ as our acid.  Consider it mixed with water:
$$\ce{HCl -&gt; H+ + Cl-}$$

When we mix these two solutions together we get:
$$\ce{Li+ + Cl- + H+ + OH- -&gt; LiCl + H2O}$$

Notice how the $\ce{OH-}$ and $\ce{H+}$ react to form $\ce{H2O}$.  The $\ce{LiOH}$ is now neutralised.

This can be written in one equation like this:
$$\ce{LiOH + HCl -&gt; LiCl + H2O}$$

Other acids could also be used to neutralise the $\ce{LiOH}$ such as $\ce{H2SO4}$:
$$\ce{2LiOH + H2SO4 -&gt; Li2SO4 + 2H2O}$$

I am uncertain of your second question.  There is no way of neutralising $\ce{MgCl2}$ as it is a neutral salt (no $\ce{OH-}$ or $\ce{H+}$).  Solubility tables (at this level) also do not affect the pH of your solution.  If you haven't learned about it yet then don't attempt to now, you will likely just confuse yourself for your test tomorrow.

I hope this has been at an appropriate level for you.