Question

Why solid propellant is not used in pslv 4th stage?

Answer 1

The PSLV-CA uses no strap-on boosters. The second stage employs the Vikas engine and carries 41.5 t (91,000 lb) of liquid propellant – unsymmetrical dimethylhydrazine (UDMH) as fuel and nitrogen tetroxide (N2O4) as oxidiser.