Explanation:
Since, the rod is present in vertical position and the spring is unrestrained. 
So, initial potential energy stored in the spring is  = 0
 = 0
And, initial potential gravitational potential energy of the rod is  .
.
It is given that, 
        mass of the bar = 0.795 kg 
             g = 9.8 
            L = length of the rod = 0.2 m
Initial total energy T = 
Now, when the rod is in horizontal position then final total energy will be as follows.
             T = 
where,    I = moment of inertia of the rod about the end = 
Also,    
where,     = speed of the tip of the rod
 = speed of the tip of the rod
               x = spring extension
The initial unstrained length is  = 0.1 m
 = 0.1 m
Therefore, final length will be calculated as follows.
               x' =  m
 m
Then,  x = 
           x =  m - 0.1 m
 m - 0.1 m
              = 0.1236 m
        k = 25 N/m
So, according to the law of conservation of energy
        
       
Putting the given values into the above formula as follows.
    
   
           v = 2.079 m/s
Thus, we can conclude that tangential speed with which end A strikes the horizontal surface is 2.079 m/s.