Molecules of hydrogen escape from earth, but molecules of oxygen and nitrogen are held to the surface and remain in the atmosphere. explain

Explanation:

Hydrogen is much lighter than oxygen and nitrogen and therefore can travel faster than both nitrogen and oxygen because of this,  it is able to escape from the the earth and not trapped by the earth Ozone dominated atmosphere.

Hydrogen molecule is lighter in weight than molecules of Oxygen and Nitrogen.

Explanation:The lighter the weight of a gaseous molecule the easier for it to float and overcome the Earth's Gravitational force or pull. Hydrogen molecule is able to escape the Earth's Gravitational pull because of its light or low molecular weight, while Oxygen and Nitrogen are heavier hence they are trapped and prevented from escaping from the Earth's Gravitational pull.

Hydrogen gas molecular weight=2.016g/mol

Oxygen gas molecular weight=16g/mol

Nitrogen molecular weight=28.018g/mol.

what is the general relationship between a galaxy's distance from earth and its speed?

the answer is:

the farther away a galaxy is from us, the faster it is moving away from us.