Given :
Number of moles , n = 36.25 mol .
Molarity , M = 1.25 M .
To Find :
The volume of water required .
Solution :
Moarity is given by :

So , 
Here , n is number of moles and M is molarity .
Putting all values in above equation , we get :

Therefore , volume of water required is 29 L .
Explanation:
The more reactive element replaces less reactive element during chemical reaction.
Since, potassium is more reactive than beryllium. When potassium reacts with beryllium choride, it replaces beryllium and forms potassium chloride and produces beryllium.
Here is your answer
B. NaCl
_________________
In option A. Na isn't present.
In option C. there are two atoms of Na
So, option B is correct
HOPE IT IS USEFUL
C = vf
c stands for the speed of waves (which is a constant that is 3 x 10^8)
v stands for the wavelength (which is given)
f stands for frequency (what we are solving for)
3 x 10^8 = (1.08 x 10^-6)f
Divide both sides by the given wavelength
f = 2.78 * 10^14 seconds