Answer:
Part a: 360000 V
Part b: no
Step-by-step explanation:
Part a: 
V = k q/r = (9^9)* (4.9^-6)/(0.05) = 360000 V 
Part b:
 the electric field on the surface of the sphere :
E=k q/r^2
 =3.6 MV/m
 therefore the air around the sphere undergoes electrical breakdown