Total density of filled ball with hydrogen gas: 
The relationship between mass and volume can be easily determined using density; for example, the mass of a body is equal to its volume multiplied by the density (M = Vd), whereas the volume is equal to the mass divided by the density (V = M/d). The ball filled with hydrogen will float in the air because total density of filled ball is lessor than the density of an air.
Density of hydrogen gas = 
Mass of the hydrogen gas : 
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Answer:
True.
Explanation:
The mass number of an atom can be calculated using no of protons and the no of neutrons.
Mass number = no of protons + no of neutrons
We can rearrange the above formula to find the no of neutrons as follows :
no of neutrons = Mass number - no of protons
or
Neutrons = Mass - protons.
Hence, the given statement is true.
A chemical reaction is the process by which a CHANGE takes place (?)