Formula of a compound is AF3. what is the valency of a

Apiece of metal with a length of 1.42 cm was measured using four different instruments. which of the following measurements is the most accurate?

How many liters of oxygen gas, at standard temperature and pressure, will react with 35.8 grams of iron metal? 4 fe (s) + 3 o₂ (g) → 2 fe₂o₃ (s)

The fact that the total amount of energy in a system remains constant is a(n)