Why are watson’s experiments considered controversial? a. his data had no practical applicability. b. they consisted strictly of correlation research. c. they cost a tremendous amount of money. d. they would be considered unethical today.

D, it is considered unethical today

John Watson's experiments are considered controversial because D. They would be considered unethical today. 

The Little Albert experiment exposed children, usually infants, first to things like rabbits, puppies, and hairballs. The children did not show fear of the items. However, once they were exposed to sudden loud sounds, rats, and stressful controlled situations. The goal of this experiment was to "condition phobia into a mentally stable child". However, these experiments are also failed in modern scientific testing. However, that doesn't make the Little Albert experiment as controversial as the unethical aspect does. 

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R₃ = 4.77 x 10⁻¹⁰ m = 0.477 nm

Explanation:

In 1913, Neil Bohr proposed an atomic model theory, based upon Quantum theory of radiation. This theory described the atomic structure, removing the defects of Rutherford's Model.

In this theory Bohr also derived the formula for the radius of nth orbit of hydrogen atom. The formula is as follows:

Rn = n²(0.53 x 10⁻¹⁰) m

Where,

Rn = Radius of nth orbit of hydrogen atom

n = no. of orbit

Therefore, for 3rd orbit

n = 3

R₃ = (3)²(0.53 x 10⁻¹⁰) m

R₃ = 4.77 x 10⁻¹⁰ m = 0.477 nm