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Chemistry Question 69 – NEET-UG 2024

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The highest number of helium atoms is in

To compare the number of atoms, convert all given quantities into moles or directly into the number of atoms.

Step 1: Understand the Goal and Key Concepts✦ Active

The question asks to identify the option containing the highest number of helium atoms. To compare, we need to convert all given quantities into a common unit, preferably moles, and then to the number of atoms using Avogadro's number (NA=6.022×1023). The atomic mass of helium (He) is approximately 4 u, meaning its molar mass is 4 g/mol. At STP (0∘C and 1 bar), the molar volume of an ideal gas is 22.7 L/mol.

💡 Teacher's Secret Hint

Remember that 'u' (atomic mass unit) refers to the mass of a single atom, while 'g/mol' refers to the mass of one mole of atoms.

Step 2: Calculate the Number of Atoms for Each Option○ Expand

Let's calculate the number of helium atoms for each option: (1) 4 u of helium: Since 1 atom of He has a mass of 4 u, 4 u of helium contains 1 atom. (2) 4 g of helium: Number of moles = massmolar mass=4 g4 g/mol=1 mol. Number of atoms = 1×NA atoms. (3) 2.271098 L of helium at STP: Number of moles = volumemolar volume=2.271098 L22.7 L/mol≈0.1 mol. Number of atoms = 0.1×NA atoms. (4) 4 mol of helium: Number of atoms = 4×NA atoms.

💡 Teacher's Secret Hint

Pay close attention to the units (u, g, L, mol) and use the appropriate conversion factors.

Step 3: Compare the Number of Atoms○ Expand

Comparing the number of atoms: (1) 1 atom (2) NA atoms (3) 0.1NA atoms (4) 4NA atoms The highest number of helium atoms is 4NA, which corresponds to option (4).

💡 Teacher's Secret Hint

Avogadro's number (NA) is a very large constant, so any quantity multiplied by NA will be significantly larger than a single atom.

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