Concept:According to Avogadro's hypothesis, samples of different molecular substances will contain the same number of molecules if they possess the exact same number of moles.
Formula:$$ \text{Moles} (n) = \frac{\text{Mass}}{\text{Molar Mass}} $$
Solution:- First, find the moles of the reference substance (\( \text{CO}_2 \)):
- \( n_{\text{CO}_2} = 11 \text{ g} / 44 \text{ g/mol} = 0.25 \text{ moles} \) (or 1/4 mole).
- Now evaluate the correct option (C) \( \text{H}_2\text{O} \):
- \( n_{\text{H}_2\text{O}} = 4.5 \text{ g} / 18 \text{ g/mol} = 0.25 \text{ moles} \) (or 1/4 mole).
- Since both equate to 0.25 moles, they contain identical numbers of molecules.
Why other options are incorrect:- 4g of \( \text{O}_2 \): \( 4/32 = 0.125 \text{ moles} \).
- 4g of O: \( 4/16 = 0.25 \text{ moles} \), BUT Oxygen atoms are not molecules. The question specifically asks for "number of molecules".
- ¼ moles of NaCl: NaCl is an ionic compound and consists of "formula units", not molecules.
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