Which describes the difference between ionic and covalent bonds? a. an ionic bond forms when molecules with like charges are attracted to each other; covalent bonds are formed when metal compounds share one or more pairs of electrons. b. an ionic bond forms when oppositely charged ions are attracted to each other; covalent bonds are formed when metals share one or more pairs of electrons. c. an ionic bond forms when molecules of opposite charges are attracted to each other; covalent bonds are formed when nonmetal compounds share one or more pairs of electrons. d. an ionic bond forms when oppositely charged ions are attracted to each other; covalent bonds are formed when nonmetals share one or more pairs of electrons.

Air is contained in a variable-load piston-cylinder device equipped with a paddle wheel. initially, air is at 400 kpa and 17°c. the paddle wheel is now turned by an external electric motor until 75 kj/kg of work has been transferred to air. during this process, heat is transferred to maintain a constant air temperature while allowing the gas volume to triple. calculate the required amount of heat transfer in kj/kg.

Antireflective coatings on solar cells are often made by applying a thin film of silicon nitride (sinx), which has an index of refractive of 1.2, on the top of the silicon solar cell, which has a refractive index of about 3.5. however, the sun emits radiation of various wavelengths which the solar cell absorbs, and the antireflective coating can only absolutely minimize the reflection of one of these wavelengths. the coating thickness is chosen to reduce the reflection of green/yellow light (e = 2.2 ev), which is the most intense color in the solar spectrum (shown below). which of the following coatings would minimize reflection of green/yellow light? the answer is 820 nm how? what is the angular width of the central maximum of an electron traveling at 2 x 108 m/s going through a single slit of width 1 mm.

Select the correct answer. what does the process of natural selection involve?