A pure substance made of two two or more elements that are chemically combined is a(n)

Which statement best describes the relationship between period and frequency of light waves? a) in wave b the period increases and the frequency decreases from wave a. b) in wave a the period increases and the frequency decreases from wave b. c) in wave b the period is shorter and the frequency is greater than in wave a. d) in wave a the period is shorter and the frequency is greater than in wave b.

All cells are made of four types of acids, lipids, proteins, and carbohydrates.

Chemistry worksheet - i am not sure what they are asking for exactly?