Mercury would have the greatest density
Answer: 1. 
2. 
Explanation:
According to the law of conservation of mass, mass can neither be created nor be destroyed. Thus the mass of products has to be equal to the mass of reactants. The number of atoms of each element has to be same on reactant and product side. Thus chemical equations are balanced.
1. Decomposition is a type of chemical reaction in which one reactant gives two or more than two products.

Thus in balanced chemical decomposition of
, the missing component is
.
2. Synthesis is a type of chemical reaction in which two reactants combine to give a single product.

Thus in balanced synthesis reaction of
, the missing component is
.
Answer:
80 MOLES OF WATER ARE PRODUCED WHEN 20 MOLES OF PROPANE ARE BURNED IN EXCESS OXYGEN ON A GAS GRILL.
Explanation:
Equation for the reaction:
C3H8 + 5 O2 ---------> 4 H2O + 3 CO2 + Heat
The above equation is in the presence of excess oxygen.
In this reaction,
1 mole of propane forms 4 moles of H2O
If 20 moles of propane were to be used, how many moles of water will be produced?
1 mole of propane = 4 moles of water
20 moles of propane = ( 4 * 20 ) moles of water
= 80 moles of water.
So, if 20 moles of propane were burned in excess oxygen, 80 moles of water will be formed. Propane is heavier than air and when properly combusted produces a large amount of heat. It is also non toxic.