Today’s postal service is more efficient than ever. Mail that once took months to move by horse and foot now moves around the country in days or hours by truck, train, and plane. If your letter or package is urgent, the U.S. Postal Service offers Priority Mail and Express Mail services. Priority Mail is guaranteed to go anywhere in the United States in two days or less. Express Mail will get your package there overnight.

This paragraph best supports the statement that

#Question id: 55

#Unit 1. Molecules and their Interaction Relevant to Biology

The standard free energy change for the reaction A → B is −15.0 kJ · mol−1. What is the equilibrium constant for the reaction at 25°C?

#Question id: 56

#Unit 1. Molecules and their Interaction Relevant to Biology

Trace elements are those required by an organism in only minute quantities. Which of the following is a trace element that is required by humans and other vertebrates, but not by other organisms such as bacteria or plants?

#Question id: 57

#Unit 1. Molecules and their Interaction Relevant to Biology

A(n) ________ has charge but negligible mass, whereas a(n) ________ has mass but no charge.

#Question id: 58

#Unit 1. Molecules and their Interaction Relevant to Biology

A covalent chemical bond is one in which ________.

#Question id: 59

#Unit 1. Molecules and their Interaction Relevant to Biology

Nitrogen (N) normally forms three covalent bonds with a valence of five. However, ammonium has four covalent bonds, each to a different hydrogen (H) atom (H has a valence of one). What do you predict to be the charge on ammonium?

#Question id: 64

#Unit 1. Molecules and their Interaction Relevant to Biology

Testosterone and estradiol are male and female sex hormones, respectively, in many vertebrates. In what way(s) do these molecules differ from each other? Testosterone and estradiol ________.