is it safe?

I can do you 60Hz appliances. What are you after? <Splutter, cough>

i just want to know if it is safe to use a portable airconditioning unit with specifications of 50 hertz frequency in 60 hertz frequency? will the motor get damaged or will it cause electrical short circuit?

50 Hz resistive appliances, such as toasters, don't care what the frequency of the lines are, but inductive loads, such as motors, will not produce as much power due to the increased frequency. Current = Voltage / impedance; impedance (of an inductive load) increases linearly with frequency.

how about a portable aircondition unit with 50 hertz frequency be used in 60 hertz frequency? is it safe? will the motor get damaged?

The motor should not be damaged, but if it runs at near full rated horsepower at 50 Hz, then it may not produce enough horsepower at 60 Hz to do the intended job. Listen to the motor when you turn it on, and if it sounds like it's straining to do the work, it may be slightly overloaded. A sure way to tell if the motor is overloaded is to let it run for a while (15-20 minutes) and check the temperature. An infrared remote thermometer is the easiest way do do that, but lacking one of those, if you can't hold your hand on the motor for more than a few seconds, then it's probably overloaded. Industrial motors are designed to run as high as 40oC above ambient, and I'd guess that hermetic compressors are designed for the same, since compressors inherently get hot by the very act of compressing gas.

ok, thank you so much!