A silicon chip used in an integrated circuit of a computer has a mass of 5.68 mg. The number of Si atoms present in the chip are:
(A) $1.22\text{x1}{{\text{0}}^{20}}$ atoms
(B) $18\text{x1}{{\text{0}}^{20}}$ atoms
(C) $\text{2}\text{.1x1}{{\text{0}}^{20}}$ atoms
(D) None of these

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Hint: Since the mass of the silicon chip is given, we need to find the number of moles of silicon present in the chip. After that we can find the number of atoms present in the chip by using the below formula:
Number of atoms = (n) x (${{N}_{A}}$)
Where,
n is the number of moles,
${{N}_{A}}$ is the Avogadro number (Value is $6.022\text{x1}{{\text{0}}^{23}}$).

Complete answer:
Silicon is widely used in the manufacture of circuit chips, transistors, diodes. The reason being that silicon is abundant in nature and a semiconductor. In addition to that silicon is easy to refine as there are less impurities; purity of about 96-97% is obtained.
It is given to us that the mass of the silicon chip is 5.68 mg. The molar mass of silicon is 28 g i.e. 28000 mg.
We will now substitute the values mentioned above in the formula to find the number of atoms of silicon present in the chip:
Number of moles of Si present(n) = $\dfrac{5.68}{28000}$
Number of atoms = (n) x (${{N}_{A}}$)
Number of atoms = ($\dfrac{5.68}{28000}$) x ($6.022\text{x1}{{\text{0}}^{23}}$)
=$1.22\text{x1}{{\text{0}}^{20}}$ atoms.

Therefore, the correct answer is option (A).

Note:
While calculating the number of moles remember to convert both the quantities to the same unit(either g or mg) and then find the number of moles. This is a common error made by many students.