This help with this chart

Explanation:

Atomic mass is the sum of number of protons and neutrons while atomic number is the number of protons or electrons.

A neutral atom has equal number of protons and electrons that's why atomic number could be either number of protons or electrons.

Element            Symbol      Atomic#      Mass#     Protons       Neutrons    

Mercury                Hg                  80            200          80                120

Solution:

number of neutrons = mass number - atomic number

number of neutrons = 200 - 80

number of neutrons = 120

Element            Symbol      Atomic#      Mass#     Protons       Neutrons    

Tungsten                 W              74                 184             74            110

Solution:

number of neutrons = mass number - atomic number

number of neutrons = 184 - 74

number of neutrons = 110

Element            Symbol      Atomic#      Mass#     Protons       Neutrons    

Sodium                 Na              11                 23             11                  12

Solution:

number of neutrons = mass number - atomic number

number of neutrons = 23 - 11

number of neutrons = 12

Element            Symbol      Atomic#      Mass#     Protons       Neutrons    

Antimony               Sb              51                122             51                  71

Solution:

number of neutrons = mass number - atomic number

number of neutrons = 122 - 51

number of neutrons = 71

Element            Symbol      Atomic#      Mass#     Protons       Neutrons    

Silver                   Ag               47                108             47                61

Solution:

number of neutrons = mass number - atomic number

number of neutrons = 108 - 47

number of neutrons = 61

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