The Question is from neet-chemistry basic-chemistry-concepts , and it was created by the author P SRAVAN KUMAR

Question

How many molecules are present in 9 g of water?

P SRAVAN KUMAR · Accepted Answer

## CORE INFORMATION
✓ **Answer**: B
## CONCEPT FRAMEWORK
 **Primary Concept**: Mole concept and Avogadro's number
 **Related Topics**: Molar mass, stoichiometry
 **Prerequisites**: Understanding of moles, Avogadro's number ($N_A = 6.022 	imes 10^{23} 	ext{ mol}^{-1}$)
## SOLUTION PATHWAY
**Given Information**:
  Mass of water = 9 g
  Molar mass of water ($H_2O$) = 18 g/mol (2 x 1 + 16 = 18)
**Method & Steps**:
 1. Calculate the number of moles of water.
  Reasoning:  The number of moles is given by the mass divided by the molar mass.
  Formula/Rule: $	ext{Number of moles} = \frac{	ext{Mass}}{	ext{Molar mass}}$
 2. Calculate the number of molecules.
  Working:  Number of moles = $\frac{9 	ext{ g}}{18 	ext{ g/mol}} = 0.5 	ext{ mol}$ 
                Number of molecules = Number of moles × Avogadro's number
                Number of molecules = $0.5 	ext{ mol} 	imes 6.022 	imes 10^{23} 	ext{ molecules/mol} = 3.011 	imes 10^{23} 	ext{ molecules}$ 
  Key Point: Avogadro's number represents the number of entities (atoms, molecules, ions, etc.) in one mole of a substance.
 3. Final step:
  Result: $3.011 	imes 10^{23}$ molecules
  Verification: The units cancel out correctly, leaving the number of molecules.
 ## OPTION ANALYSIS
A :x: This is Avogadro's number, representing the number of molecules in 1 mole of water, not 0.5 moles.
B ✓: This is the correct number of molecules calculated from 0.5 moles of water.
C :x: This is double the correct answer, suggesting a mistake in the calculation (perhaps using 1 mole instead of 0.5 moles).
D :x: This is triple the correct answer, indicating a significant error in the calculation.
 ## LEARNING AIDS
 **Common Mistakes**:
  1.Incorrect molar mass: Using an incorrect molar mass for water will lead to an incorrect number of moles and molecules.
  2.Forgetting Avogadro's number: Failing to multiply the number of moles by Avogadro's number will result in an answer with incorrect units and magnitude.
 **Quick Tips**:
  1.Always double-check the molar mass and ensure you are using the correct units.
  2.Remember Avogadro's number is a constant that relates moles to the number of entities.

P SRAVAN KUMAR · Answer

$6.022 	imes 10^{23}$

P SRAVAN KUMAR · Answer

The correct Option is "$3.011 	imes 10^{23}$"

P SRAVAN KUMAR · Answer

$1.204 	imes 10^{24}$

P SRAVAN KUMAR · Answer

$1.806 	imes 10^{24}$

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