A convergent – divergent nozzle is said to chocked when

Question

Consider the following statements:

A convergent – divergent nozzle is said to chocked when              

1. Critical pressure is stained at th throat
2. Velocity at throat becomes sonic
3. Exit velocity becomes supersonic

Which of these statements are correct?

(a) 1,2 and 3                     (b) 1 and 2

(c) 2 and 3                         (d) 1 and 3