Your list of choices is a very short list, and doesn't include any 
correct explanation.
The mass of an atom is roughly the number of protons AND neutrons 
in its nucleus, but the element only depends on how many protons are there.  
Different atoms of the same element may have different numbers of 
neutrons, so their masses are different.  But they're the same element, 
because they all have the same number of protons.
        
             
        
        
        
Answer:
kftisgkstisirstizurzursrus
 
        
             
        
        
        
Answer:
50 watts
Explanation:
Applying,
Power (P) = Workdone (W)/Time(t)
But,
Work done (W) = Force (F)×distance(d)
Therefore, 
P = Fd/t..................... Equation 1
Where P =  power of the weightlifter, F = Force applied, d = distance, t = time.
From the question,
Given: F = 200 N, d = 0.5 m, t = 2 s
Substitute these values into equation 1
P = (200×0.5)/2
P = 100/2
P = 50 watts