I have a few questions.

1. write the net ionic equation for a precipitate when solutions of magnesium nitrate and potassium hydroxide form.
When I did this equation out, both products were soluble. Am I doing this wrong?

2. A 50.00 mL sample of .0250 M silver nitrate is mixed with .0400 M chromium (II) chloride. What is the minimum volume of chromium (II) chloride required to fully precipitate silver chloride?
I have the balanced equation done, but I'm stuck as to where to start. Can someone give me a brief idea as to where to start/go?

3.For acid-base reactions, what is the reacting species, that is, the ion or molecule that appears in the chemical equation, in the following acids?
What exactly is the reacting species? One of the acids given is perchloric acid, and the answer is given as H+. Why is this the answer, and not ClO4-? Basically, what is the reacting species and how can I tell what it is?

Magnesium hydroxide is NOT soluble. Milk of Magnesia (magnesium hydroxide) is, well, you know, not a clear solution: it is a solid suspension in water. And tastes ugh.

Balance the equation on 2). Then, figure the moles of silver nitrate. From the balance equation, how many moles of CrCL2 is needed?

Acids are defined as proton donors, so the H+ is the reacting species. The reacting species is the thing that causes the predominate driving reaction.

Oops, I just realized I had figured the first question out already - thank you.

I need to write the net ionic equation for Ag2SO4 + BaCl2 -> 2AgCl + BaSO4.
Ag2SO4 is slightly soluble, according to the solubility charts that I've seen. How do I determine whether it is weak or strong so that I can write the equation?

I would write Ag2SO4 as the ions as well as BaCl2. AgCl an BaSO4 are solids.

BaCl2

BaCl2 would dissociate into Ba2+ and 2Cl- ions.