Which of the following are correct regarding the mole and Avogadro constant? 1. The Avogadro constant is a dimensionless quantity. 2. One mole…

The correct option is

2 only

Explanation

The mole is the SI base unit for the amount of substance. In 2019, the definition of the mole was revised by the General Conference on Weights and Measures (CGPM). It is no longer defined based on the mass of Carbon-12 but is instead defined by fixing the numerical value of the Avogadro constant.

Statement-wise Analysis:

• Statement 1 is Incorrect: According to the 2019 redefinition of SI units, one mole contains exactly 6.02214076 × 10²³ elementary entities. This number is the fixed numerical value of the Avogadro constant, N_A, when expressed in the unit mol⁻¹.
• Statement 2 is Correct: The Avogadro constant is not a dimensionless quantity; it has the unit of reciprocal mole (mol⁻¹). It represents the number of constituent particles per mole. In contrast, the Avogadro number refers specifically to the numerical value (6.022... × 10²³) and is dimensionless, but the constant itself carries units.
• Statement 3 is Incorrect: The standard symbol for the physical quantity "amount of substance" is n. The symbol 'A' typically denotes the Ampere (unit of electric current) or Mass Number in atomic physics. The unit for the amount of substance is the mole (symbol: mol).

Key Takeaway:
The mole is defined by a fixed numerical constant (Avogadro constant, N_A), which has the unit mol⁻¹. The symbol for the amount of substance is n.