The actual answer is B) Chlorine
According to the Bohr Model diagram, the atom has seventeen electrons. This makes it Chlorine.
Sorry if i'm late!!
 
        
                    
             
        
        
        
Answer:
A
Explanation:
A and B are isotopes of one another but the same element
C and D are isotopes of one another but the same element
However, A and B have a different proton count than C and D, indicating different elements because the proton count is equivalent to the atomic number.
 
        
                    
             
        
        
        
Answer:
3099 J
Explanation:
The increase in thermal energy corresponds to the mechanical energy lost in the process.
The mechanical energy is given by the sum of gravitational potential energy and kinetic energy of the fireman:

At the top of the pole, the fireman has no kinetic energy, so all his mechanical energy is just potential energy:

When the fireman reaches the bottom, he has no gravitational potential energy, so his mechanical energy is just given by his kinetic energy:

So, the loss in mechanical energy was

and this corresponds to the increase in thermal energy.