It is a standard choosen.We can choose some other frequency.
If we change the frequency the power system will be 
disrupted,the instruments&appliances has to be designed 
accordingly.

yes we can choose but the some what high  frequncy will 
required low volt becuase pressure for electron flow 
already affected by high freq. and vice versa

if we choose other freequency suppose 60hz ,our standara 
freequency is 50hz.for transfer of power there must be same 
freequency.Also if freequency increases number of poles 
also increases,if poles inc.d diameter of equipment also 
inc.it leads to high cost.

50HZ is the standard our system has decided, so why you want
to disturb the system?? Your source with about 2% above and
lower than standard freq. can not be synchronized wit the
system.

IN INDIA THERE IS A STANDARD FREQUENCY IT IS 50HZ BUT IN 
OUTHER COUNTRYS IT IS 60HZ IT IS STANDARD

For a Electrical system to get synchronised, one of the 
condition to get satisfy is the system frequency.
If frequency to be changed , then it is to be considered 
right from power generation system.
While changing the frequency of the stationthe following 
factors to be considered.
Frequency = 12o*poles/speed of the machine.
If this frequency factor to get change.....then pole of the 
machine and the speed of the machine has to design 
accordingly, which is quite inefficient and many factors to 
be further considered.

The reason why in our country we are generating and 
distributing the power with 50Hz/sec is, when frequency 
increases say 60Hz/sec the losses in transmission and 
distribution, transformers and active loads will be high.  
economically 60Hz/Sec not affordable in our country. 
because copper very high in cost.

in orfer to increase freq. wehave to increase the turbine
speed in power generating station. for that we need some
what more fuel(for diesel turbine) or water (for water
turbine). so it may lead coat effective.

It is a traditional system which has been established. all 
the euipments are designed on the basis of 50 Hz so if we 
change the freqency all the equipmets get damaged so we can 
not change the frequency.

Yes we can use another frequency but for this change we have
to change in our power system such as
(1) As we know in generating stations the alternator is used
for producing electric energy and its frequency is given by
            f= (Ns)*P/120
where Ns is synchronous speed and P is number of poles so
for increasing the frequency we have to increase the number
of poles which becomes very costly & so uneconomically
And another reason is that we used electrical instrument
which are standardized at 50 hz, 230 v
so we have to also change our electrical systems which are
also very costly
so this is only standard value we can change it but it is
very uneconomical

all above answers are correct in its place but we forget 
basic thing when we design any system following parameters 
are to be taken into considaration
1.avrage temp.
2.avrage sea lavel
3.windvelocity
4.distance
5.size
considering all these factors 50HZ frequency is most 
economical system thats why we use 50Hz

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.