Final answer:
Each triple bond in a hydrocarbon molecule reduces the number of hydrogen atoms by four because each carbon atom in the triple bond loses two possible bonds with hydrogen, due to its bonding capacity.
Step-by-step explanation:
The student's question is related to organic chemistry and specifically to the concept of hydrocarbons and their structural formulas. In organic chemistry, a triple bond within a molecule will reduce the number of hydrogen atoms by four. This is because a carbon atom can make a maximum of four bonds. When forming a triple bond with another carbon, only one additional bond can be formed by that carbon atom, typically with hydrogen. However, if a carbon formed only single bonds, it could bond with four hydrogen atoms. Therefore, each triple bond between two carbon atoms effectively removes the possibility of two carbon-hydrogen bonds on both of the carbon atoms involved in the triple bond, leading to a reduction of four hydrogen atoms in total.
For example, in ethene (C2H4), each carbon atom forms a double bond with the other and two single bonds with hydrogen atoms. If we turned this double bond into a triple bond to form ethyne (C2H2), each carbon would lose one of its hydrogen atoms due to this bonding change, hence reducing the total number of hydrogen atoms by two for each carbon, or four in total.