From 320 mg. of `O_(2), 6.023 xx 10^(20)` molecules are removed, the no. of moles remained are

Options

A. `9 xx 10^(-3)` moles
B. `9 xx 10^(-2)` moles
C. Zero
D. `3 xx 10^(-3)` moles

Explanation

To solve the problem step by step, we will follow the calculations as outlined in the video transcript.

### Step 1: Convert the mass of O₂ from milligrams to grams
Given mass of O₂ = 320 mg

To convert milligrams to grams:
\[ 320 \text{ mg} = 320 \times 10^{-3} \text{ g} = 0.32 \text{ g} \]

### Step 2: Calculate the number of moles of O₂ in 0.32 g
The molar mass of O₂ (oxygen) is 32 g/mol.

Using the formula for moles:
\[ \text{Number of moles} = \frac{\text{mass (g)}}{\text{molar mass (g/mol)}} \]
\[ \text{Number of moles of O₂} = \frac{0.32 \text{ g}}{32 \text{ g/mol}} = 0.01 \text{ moles} \]

### Step 3: Convert the number of molecules removed to moles
We are given that \(6.023 \times 10^{20}\) molecules are removed.

Using Avogadro's number, which is approximately \(6.022 \times 10^{23}\) molecules/mol, we can convert molecules to moles:
\[ \text{Number of moles removed} = \frac{6.023 \times 10^{20} \text{ molecules}}{6.022 \times 10^{23} \text{ molecules/mol}} \approx 0.001 \text{ moles} \]

### Step 4: Calculate the remaining number of moles of O₂
Now, we subtract the moles of O₂ removed from the initial moles:
\[ \text{Remaining moles} = \text{Initial moles} - \text{Moles removed} \]
\[ \text{Remaining moles} = 0.01 \text{ moles} - 0.001 \text{ moles} = 0.009 \text{ moles} \]

### Step 5: Express the remaining moles in scientific notation
\[ 0.009 \text{ moles} = 9 \times 10^{-3} \text{ moles} \]

### Final Answer
The number of moles of O₂ remaining is \(9 \times 10^{-3} \text{ moles}\).

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