Here is the calculation for part a) using $k = 9 \times 10^9 \text{ N m}^2/\text{C}^2$. a) Calculate the magnitude of the electrostatic force between an electron and a proton. Given: • Coulomb's constant, $k = 9 \times 10^9 \text{ N m}^2/\text{C}^2$ • Elementary charge (magnitude), $e = 1.602 \times 10^{-19}$ C • Charge of electron, $q_e = -1.602 \times 10^{-19}$ C • Charge of proton, $q_p = +1.602 \times 10^{-19}$ C • Distance, $r = 1.0 \times 10^{-10}$ m (from the original problem statement) Step 1: Use Coulomb's Law to find the magnitude of the electrostatic force. $$F = k \frac{|q_e q_p|}{r^2}$$ Step 2: Substitute the given values into the formula. $$F = (9 \times 10^9 \text{ N m}^2/\text{C}^2) \frac{|(-1.602 \times 10^{-19} \text{ C})(+1.602 \times 10^{-19} \text{ C})|}{(1.0 \times 10^{-10} \text{ m})^2}$$ Step 3: Calculate the force. $$F = (9 \times 10^9) \frac{(1.602 \times 10^{-19})^2}{(1.0 \times 10^{-10})^2} \text{ N}$$ $$F = (9 \times 10^9) \frac{2.566404 \times 10^{-38}}{1.0 \times 10^{-20}} \text{ N}$$ $$F = (9 \times 10^9) \times (2.566404 \times 10^{-18}) \text{ N}$$ $$F = 23.097636 \times 10^{-9} \text{ N}$$ $$F = 2.3097636 \times 10^{-8} \text{ N}$$ Rounding to three significant figures: $$F \approx \boxed{\mathbf{2.31 \times 10^{-8} \text{ N}}}$$ That's 2 down. 3 left today — send the next one.