Question

Question 2.44 An ion with mass number 56 contains 3 units of positive charge and 30.4% more neutrons than electrons. Assign the symbol to this ion.

Class XI Structure of Atom Page 67

Answer 1

Let the number of electrons present in ion ,S3+ = x

∴ Number of neutrons in it = x + 30.4% of x = 1.304 x

Since the ion is tripositive,

⇒ Number of electrons in neutral atom = x + 3

∴ Number of protons in neutral atom = x + 3

Now mass number = no of protons + no of neutrons

56 = x + 3 + 1.304x

Or 2.304x = 53

Or x = 23

Therefore no of protons = atomic no = x + 3 = 23 + 3 = 26

Answer 2

Let the number of electrons in an ion = x
so, number of electrons in neutral atom = x +3 [ because ion have 3 unit positive charges ]
because in neutral atom,
number of electrons = number of protons
so, number of protons in neutral atom = x + 3

now, A/C to question,
number of neutrons = number of electrons + 30.4 % of number of electrons
= x + 304x/1000 = 1.304x

we know,
mass number = number of protons + number of neutrons
56 = x + 3 + 1.304x
56 - 3 = 2.304x
53/2.304 = x = 23.003 ≈ 23
hence, number of protons = 23 + 3 = 26
it means elements is Fe.
therefore, symbol of the ion is ⁵⁶₂₆Fe³⁺