How many moles are present in 7.5 × 10^{19} molecules of ammonia (NH_3)?

• A. 1.25 × 10^{-4} mol
• B. 7.5 × 10^{-19} mol
• C. 4.52 × 10^{-5} mol
• D. 6.02 × 10^{23} mol

Answer: (A)

Verified step by step guidance

1. Identify the given quantity: 7.5 \times 10^{19} molecules of ammonia (NH_3).
2. Recall that 1 mole of any substance contains Avogadro's number of molecules, which is approximately 6.022 \times 10^{23} molecules/mol.
3. Set up the conversion to find moles from molecules using the formula: \(\text{moles} = \frac{\text{number of molecules}}{\text{Avogadro's number}}\).
4. Substitute the given values into the formula: \(\text{moles} = \frac{7.5 \times 10^{19}}{6.022 \times 10^{23}}\).
5. Perform the division of the coefficients and subtract the exponents in the powers of ten to express the answer in scientific notation.