Question

For Fe, its atomic number is 26 and its mass number is 56. How many neutrons does it have?
A 26
B 30
C 56
D 82

PLATO

Answer 1

Mass Number (given as 56) = # of protons + # of neutrons

Atomic Number (given as 26) = # of protons

Plug in values to first equation:
56 = 26 + n (where n equals to # of neutrons)

Solve for n (subtract 26 from both sides)
56 - 26 = n

Answer: n = 30

Answer 2

Answer : The correct option is, (B) 30

Explanation :

Atomic number : It is defined as the number of protons or number of electrons.

Atomic number = number of protons = number of electrons

Atomic mass : It is defined as the sum of number of protons and number of neutrons.

Atomic mass = Number of protons  + Number of neutrons

or,

Atomic mass = Atomic number  + Number of neutrons

As we are given that,

The element is. Fe

Atomic number = 26

Mass number or atomic mass = 56

Atomic mass = Atomic number  + Number of neutrons

Number of neutrons = Atomic mass - Atomic number

Number of neutrons = 56 - 26

Number of neutrons = 30

Therefore, the number of neutrons are, 30