Can resonance increase frequency?
The resonant frequency of an LC circuit is given by

$$ f = \frac {1}{2 \pi \sqrt {LC}} $$

and plugging in the values you have chosen gives

$$ f = \frac {1}{2 \pi \sqrt {0.1 \cdot 100 \mu}} = \frac {1}{2 \pi \cdot 0.00316 } =  50.3~Hz$$

So your resonant frequency is almost exactly on the mains frequency of 50 Hz.


  
  Why does resonance increases the voltage?
  


It's like pushing a swing or pendulum. If you do it at the natural frequency of oscillation and at the right point in the cycle then every push will boost a little bit more. In the case of the pendulum or swing air resistance will eventually limit the amplitude of the oscillation. In the LC circuit the internal resistance will cause losses which increase with increasing amplitude until an equilibrium is reached.


  
  Why the voltage does not increase at a frequency of say 2 KHz?
  


See the formula.


  
  If I made this experiment practically, Will the transformer wear out?
  


Transformers lifespan is mostly determined by temperature which is usually a result of too-much current or insulation breakdown which is a result of too high a voltage being applied. You would need to know the winding insulation breakdown voltage to figure that out. At 50 V you are unlikely to have a problem.