Answer: The correct option is 3.
Explanation: We are given a compound which is made up of iron and oxygen only. The ratio of the two are given as:

This means that, number of iron ions are 2
Number of oxide ions are 3
From the above information, the formula becomes : 
The valency of iron = 3
Valency of oxide = 2
This compound is named as iron (III) oxide.
Hence, the correct option is 3
Answer:
0.375 grams are needed to make 25 mL solution.
Explanation:
Mass of
cuprous nitrate required to make 1 l of solution = 15 g.
1 L = 1000 mL
Mass of
cuprous nitrate required to make 1000 mL of solution = 15 g
Mass of
cuprous nitrate required to make 1 mL of solution:

Mass of
cuprous nitrate required to make 25 mL of solution:

0.375 grams are needed to make 25 mL solution.
Answer:
168.0 g
Explanation:
First thing, write a balanced chemical equation:

n(H2SO4) = concentration * volume
= 1.0 M * 2.0 L
= 2.0 mol
According to the balanced equation, 1 mol of acid requires 2 mol of sodium bicarbonate. This means that 2 mol of acid requires 2 mol of sodium bicarbonate. What mass of sodium bicarbonate is this?
mass (NaHCO3) = number of moles * molar mass
= 2.0 mol * 84.0065 g/mol
= 168.0 g
Answer:
magnesium atom
The most common and stable type of magnesium atom found in nature has 12 protons, 12 neutrons, and 12 electrons