1.563 x1030 formula units of barium nitrate contains how many individual nitrate ions?
Barium nitrate has the formula
This means that each formula unit of barium nitrate contains two nitrate ions. The number of nitrate ions in 1.563x10^30 is thus 2(1.563x10^30), or 3.126x10^30 individual nitrate ions.
When you're trying to solve a problem like this, write out the formula for the ionic compound. The barium ion, being in Group 2 of the periodic table, forms an ion with a charge of +2. Nitrate is a polyatomic ion. One way to know this is that it ends in -ate. Monatomic ions (those with just one element) end in -ide if they have a negative charge. You can find the nitrate ion, NO3-, on a table of polyatomic ions and see that its charge is -1. An ionic compound has a net charge of zero, so the formula will have to contain 2 nitrate ions to cancel out the +2 charge of the barium ion.