To solve this problem, we need to analyze each statement about lipids and determine their correctness:$\newline \bullet$(a) Lipids having only single bonds are called unsaturated fatty acids.$\newline$ - This statement is incorrect. Lipids with only single bonds are called saturated fatty acids. Unsaturated fatty acids contain one or more double bonds.$\newline \bullet$(b) Lecithin is a phospholipid.$\newline$ - This statement is correct. Lecithin is indeed a type of phospholipid, commonly found in egg yolks and soybeans.$\newline \bullet$(c) Trihydroxy propane is glycerol.