AP Chemistry Question of the Day --23

Welcome back to my blog. Here comes the answer to question 22 I posted yesterday. The correct answer is C. 

The Energies of visible and ultraviolet light photons are comparable with the electron energy level differences in atoms and molecules. When electron is excited from ground state or lower energy level to a higher energy level, energy needs to be absorbed. When electron goes from a higher energy level to a 

lower energy level, energy will be released. Thus, C is the correct answer.

When molecules vibrate, they absorb energy from the infrared region. So, answer A is not correct. Answer B is related to ionization energy. Molecular mass has no direct relationship with energies. Both B and D are incorrect.

 Following is Question 23 of the series. 

23. 

To make Au stronger and harder, it is often alloyed with other metals, such as Cu and Ag. Consider two alloys, one of Au and Cu and one of Au and Ag, each with the same mole fraction of Au. If the Au/Cu alloy is harder than the Au/Ag alloy, then which of the following is the best explanation based on the information in the table above?

(A) Cu has two common oxidation states, but Ag has only one.
(B) Cu has a higher melting point than Au has, but Ag has a lower melting point than Au has.
(C) Cu atoms are smaller than Ag atoms, thus they interfere more with the displacement of atoms in the alloy.
(D) Cu atoms are less polarizable than are Au or Ag atoms, thus Cu has weaker interparticle forces.

I will post the answer and explanation tomorrow. 

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