To solve this problem, we need to analyze each option regarding the characteristics of cockroaches:$\newline \bullet$Option 1: A ring of gastric caeca is present at the junction of midgut and hindgut.$\newline$ - This statement is incorrect.$\newline$ - In cockroaches, the gastric caeca are actually located at the junction of the foregut and midgut, not at the midgut and hindgut.$\newline \bullet$Option 2: Hypopharynx lies within the cavity enclosed by the mouth parts.$\newline$ - This statement is correct.$\newline$ - The hypopharynx is a structure that acts like a tongue and is located within the cavity formed by the mouthparts of the cockroach.$\newline \bullet$Option 3: In females, 7th, 9th sterna together form a genital pouch.$\newline$ - This statement is incorrect.$\newline$ - In female cockroaches, the 7th, 8th, and 9th sterna together form the brood or genital pouch, not just the 7th and 9th.$\newline \bullet$Option 4: 10th abdominal segment in both sexes, bears a pair of anal cerci.$\newline$ - This statement is correct.$\newline$ - Both male and female cockroaches have a pair of anal cerci on the 10th abdominal segment.$\newline$Based on the analysis, the incorrect characteristic with respect to cockroach is given in Option 1.