The total surface area of an open pipe of length H cm, external radius R cm and internal radius r cm, is :

1. πR² - πr² + 2π(R - r)H

2. 2πR² - 2πr² + 2πRH

3. 2πRH - 2πrh + πR² - πr²

4. 2(πR² - πr²) + 2πRH + 2πrH

Given,

External radius = R cm,

Internal radius = r cm,

Height = H cm.

Total surface area of hollow cylinder = External curved surface area + Internal curved surface area + 2(Area of cross section)

= 2πRH + 2πrH + 2(πR² - πr²).

Hence, Option 4 is the correct option.