The atomic number for Pb is 82
∴ Pb has 82 protons and 206-82 = 14 protons
The actual mass of Pb nuclei is
=(82 × mass of the proton) + (124 × mass of neutron)
=(82× 1.00728) + (124 × 1.008664) amu
= 207.6713 amu
The mass of lead which is given is 205.9744 amu
∴mass defect is
m = 207.6713 - 205.9744 = 1.6969 amu
=1.6969 × 1.66054 × 10⁻²⁷kg
=2.818 × 10⁻²⁷kg
The binding energy is E = mc²
C is the speed of light in vacuum = 2.9979 × 10⁸m/s
∴ E = 2.532 × 10×⁻¹⁰ J/mol
= 2.532 × 10⁻¹⁰ × 6.023 × 10²³ J/mol
= 1.53811 × 10¹⁴ J/mol
Number of moles is defined as the ratio of given mass in g to the molar mass.
The mathematical formula is:
Number of moles =
(1)
Number of zinc atoms is equal to
, by Avogadro number, number of moles can be calculated.
As, 1 mol=
atoms, hence,

= 0.2822 mol
Now, from formula (1), calculate mass in g (molar mass of zinc = 65.4 g/mol)
0.2822 mol =
mass in g = 
= 18.45588 g
Thus, by rounding off the above number, it will come near about 19 g approximately.
Hence, option (C) is the correct answer.
Molecules may be similar or different on the basis of size, shape, structure and chemical composition.
<h2>Similarities and differences</h2>
Two molecules can be considered similar or different on the basis of size, shape, structure and chemical composition. The molecules in the two proposed systems are consider the same when they are similar in size, shapes, structure and chemical composition.
While on the other hand, the molecules is considered different when they have different structure and chemical composition so we can say that molecules may be similar or different on the basis of size, shape, structure and chemical composition.
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