How many moles of Kr are present in 398 mg of Kr? (Molar mass of Kr = 83.8 g/mol)

• A. 4.75 mol
• B. 0.0475 mol
• C. 0.475 mol
• D. 0.00475 mol

Answer: (D)

Verified step by step guidance

1. Convert the mass of krypton (Kr) from milligrams to grams because the molar mass is given in grams per mole. Use the conversion factor: 1000 mg = 1 g. So, calculate the mass in grams as \(\text{mass (g)} = \frac{398}{1000}\).
2. Recall the formula to calculate moles from mass and molar mass: \(\text{moles} = \frac{\text{mass (g)}}{\text{molar mass (g/mol)}}\).
3. Substitute the values into the formula: \(\text{moles} = \frac{\text{mass in grams}}{83.8}\), where 83.8 g/mol is the molar mass of Kr.
4. Perform the division to find the number of moles of Kr present in the given mass.
5. Compare your calculated value with the provided options to identify the correct number of moles.