Question : 

WHY THE FREQUENCY IS 50 HZ IN INDIA
 
Ans: The material properties of ferromagnetic substances 
having great importance in selecting frequency. Frequency 
range from 45 Hz to 70 Hz is useable region.
Another consideration is the core and copper loss. In core 
loss, the power loss is proportional to frequency, and for 
copper loss, is proportional to sq.of frequency.
Developing countries like India, defenitely select the 
chepest option, thats 50 HZ.
Another consideration is equipment availablity.
Equipment availibility is only in the range of 50 Hz and 60 
Hz. If we chose some other frq. say 70 Hz, Indian 
manufactures has to produce accordingly, and that will 
create less utilization of ferro magnetic materials.

From above, the conclusion is 50Hz is most suitable and 
economical option.