Statement I : Comets revolve round the Sun only in long elliptical orbits. Statement II : A comet develops a tail when it gets close to the Sun.

Statement I is false because comets do not revolve around the Sun 'only' in long elliptical orbits. While many comets have highly elliptical orbits [1], they are also classified into periodic, non-periodic, parabolic, and hyperbolic groups. Parabolic and hyperbolic comets possess enough speed to be ejected from the solar system, meaning their paths are not closed elliptical orbits. Statement II is true; as a comet approaches the Sun, solar heat causes its icy nucleus to sublimate. This process of outgassing creates a visible atmosphere called a coma and often a glowing tail of ionized plasma and dust [2]. The tail develops due to the effects of solar radiation pressure and solar wind acting upon the nucleus as it warms in the inner solar system [2]. Since Statement I is factually incorrect due to the word 'only', the correct option is 4.

Sources

1. [1] Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 2: The Solar System > Comets > p. 33
2. [2] Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 2: The Solar System > 2. The Solar system > p. 35