Which of the following statements is TRUE for all saturated hydrocarbons?

The correct option is: They show substitution reactions rather than addition reactions.

Understanding Saturated Hydrocarbons:
Saturated hydrocarbons, commonly known as alkanes, are organic compounds consisting entirely of single covalent bonds between carbon atoms ($\text{C}-\text{C}$) and between carbon and hydrogen atoms ($\text{C}-\text{H}$). Because all available valence electrons of the carbon atoms are fully utilized forming single bonds, these molecules are "saturated" with hydrogen and cannot bond with any additional atoms without breaking an existing single bond.

Analysis of Options:

1. "They are generally very reactive due to triple bonds." - False. Hydrocarbons with triple bonds are called alkynes, which are unsaturated. Saturated hydrocarbons contain only single bonds and are relatively unreactive (paraffins).

2. "They readily undergo addition reactions." - False. Addition reactions require unsaturated carbon-carbon double or triple bonds to break open and accept new atoms. Saturated hydrocarbons do not have double or triple bonds.

3. "They contain at least one double bond." - False. Hydrocarbons containing double bonds are alkenes, which are unsaturated.

4. "They show substitution reactions rather than addition reactions." - True. Since all bonds are single bonds and the molecule cannot accept extra atoms without losing existing ones, saturated hydrocarbons undergo substitution reactions (such as chlorination of methane in the presence of sunlight), where one atom or group is replaced by another atom or group.