Which molecule contains ten hydrogen atoms

Butane  

Step-by-step explanation:

Butane is an alkane.  

The general formula for an alkane is CₙH₂ₙ₊₂.

Butane has four carbon toms, so its formula is C₄H₁₀.

Propane is wrong. It has three carbon atoms, so its formula is C₃H₈.

Butene is wrong. The general formula for an alkene is CₙH₂ₙ, so the formula is C₄H₈.

Propene is wrong. It has three carbon atoms, so its formula is C₃H₆.

since the atomic number is the number of protons in the nucleus, as we move to the left on the periodic table, the electrostatic pull between the nucleus and the valence electron shell decreases. as we move down a group (vertical column), the valence shell energy level gets further and further from the nucleus.