In Bohr's model of the hydrogen atom, the radius of an orbit

a. is proportional to n2.

b. is smallest for the highest energy state.

c. increases when a photon of light is emitted from an excited atom.

d. can have any value that is larger than the ground-state radius.

e. none of the above

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To determine the correct answer among the given options, let's break down each option and analyze its accuracy in relation to Bohr's model of the hydrogen atom:

a. According to Bohr's model, the radius of an orbit is determined by the principal quantum number (n), and the formula for the radius is given by r = 0.529 * n^2 / Z, where Z is the atomic number. Therefore, option a is indeed correct since the radius is proportional to n^2.

b. The energy of an electron in Bohr's model is inversely proportional to the square of its orbit radius. Hence, the highest energy state corresponds to the largest orbit and, therefore, the largest radius. Consequently, option b is not accurate, making it incorrect.

c. When a photon of light is emitted from an excited atom, the electron transitions from a higher energy state to a lower energy state, which corresponds to a smaller orbit radius in Bohr's model. Thus, option c is incorrect.

d. According to Bohr's model, the orbits of the hydrogen atom are quantized, meaning they can only have specific discrete values determined by the principal quantum number (n). The ground-state radius is the smallest possible value for the orbit radius. Hence, option d is incorrect.

e. After analyzing options a, b, c, and d, we can conclude that none of the above options accurately describes Bohr's model of the hydrogen atom. Therefore, the correct answer is e. None of the above.

In summary, the correct answer is e. None of the above.