Answer:
 Volume of balloon = 1000 cm^3
Step-by-step explanation:
 The head of a normal person can be assumed as a sphere with radius 10 cm.
 Volume of sphere 
, where r is the radius.
 We have approximate radius = 10 cm.
 Approximate volume of head 

 In the given options the closest value to the approximate volume is 1000 cm^3.
 So, volume of head = Volume of balloon = 1000 cm^3