name the following compound and why--- Mg(OH)subscript 2 and NO subscript2 and SnOsubscript 2?

Answer 1

Mg(OH)2 = Magnesium Hydroxide
OH is hydroxide - it's a common anion. Mg is magnesium. That one was simple enough.

NO2 = Nitrogen Dioxide (or nitrous oxide - laughing gas) - although the ion NO2- is nitrite
Technically, when you have two non-metals, you use prefixes to indicate the number of a particular atom. So you could also name it mononitrogen dioxide although most leave off the mono if it is on the first atom. (mono = 1; di = 2; tri = 3, etc.) If NO2 has a single negative charge, it is also a common anion called nitrite.

SnO2 = Tin (IV) Oxide
When you deal with ions, you do not need to follow the rules I mentioned earlier (mono, di, etc.). However, Tin is a transition metal which means its ion state changes. To determine which Sn it is, look at how many O were needed. It used 2 O, each of which has a 2- charge. 2 x 2 = 4. So total it has a 4- charge. Thus, Tin needs a 4+ charge. To indicate that you call it Tin (IV).

Answer 2

MgOH2 = Magnesium Hydroxide

NO2 = Nitrous Oxide (Laughing Gas)

SnO2 = Tin Oxide

I'm no PhD Chemist, but I'm pretty sure they are right.