The assertion is true, and the reason is a correct explanation; saturated hydrocarbons are less reactive because all carbon valencies are satisfied by single covalent bonds, providing stability.
The assertion that saturated hydrocarbons are chemically less reactive is supported by the reason that all the valencies of carbon atoms in these compounds are satisfied by single covalent bonds. Saturated hydrocarbons consist of carbon-carbon and carbon-hydrogen single bonds, leading to a molecular structure where each carbon atom is surrounded by the maximum number of hydrogen atoms. This arrangement follows the principle of achieving a stable, fully saturated configuration, known as the tetrahedral geometry.
The saturated nature of these hydrocarbons implies that there are no available or unsaturated sites for additional chemical reactions, as all carbon valencies are already engaged in strong single bonds. This structural stability makes saturated hydrocarbons less prone to undergo chemical reactions compared to unsaturated hydrocarbons, which contain double or triple bonds. The absence of readily available pi bonds in saturated hydrocarbons limits their reactivity, making them relatively inert under normal chemical conditions. Therefore, the reason provided aligns with the observed lower reactivity of saturated hydrocarbons due to the saturation of carbon valencies with single covalent bonds.