Given the following measured values for masses:

- Proton: $1.67262 \times 10^{-27}$ kg
- Neutron: $1.674927 \times 10^{-27}$ kg
- Electron: $9.109 \times 10^{-31}$ kg

Determine the expected mass of an atom of $\text{40Ar}$ (it contains 18 protons, 22 neutrons, and 18 electrons) to the appropriate number of significant figures.

a. $6.697 195 \times 10^{-26}$ kg
b. $6.697 \times 10^{-26}$ kg
c. $6.69720 \times 10^{-26}$ kg

To calculate the expected mass of an atom of 40Ar, multiply the mass of each particle by the number of that particle and sum the masses. The correct answer is option c. 6.69720 E-26.

To find the expected mass of an atom of 40Ar, we need to add up the masses of its constituent particles: protons, neutrons, and electrons. The atomic number of 40Ar is 18, which means it has 18 protons. The number of neutrons is given as 22. The mass of a proton is 1.67262 × 10⁻²⁷ kg, the mass of a neutron is 1.674927 × 10⁻²⁷ kg, and the mass of an electron is 9.109 × 10⁻³¹ kg.

To calculate the total mass, we multiply the mass of each particle by the number of that particle and then sum these masses. Multiplying the mass of a proton by 18, the mass of a neutron by 22, and the mass of an electron by 18, and then summing these results, gives us the expected mass of an atom of 40Ar: 6.69720 × 10⁻²⁶ kg. Therefore, the correct answer is option c. 6.69720 E-26 when rounded to the appropriate number of significant figures.

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