Question

1. what group of elements accounts for more than 98% of the human body by weight? a. carbon, hydrogen, oxygen, nitrogen. b. calcium, hydrogen, oxygen, nitrogen. c. carbon, phosphorus, oxygen, hydrogen. d. calcium, phosphorus, hydrogen, nitrogen. 13. which of the following best describes the reaction h₂co₃ → h₂o + co₂? a. decomposition reaction b. exchange reaction c. reversible reaction d. synthesis reaction 14. what are electrolytes? a. compounds that form covalent bonds with water. b. compounds that ionize in water. c. compounds that alter ph of the solution they are in are electrolytes. d. compounds that release radioactive radiation. 15. what is the most abundant inorganic substance in the body? a. glucose b. water c. lipid d. dna 16. which of the following is true regarding the ph scale? a. each whole number on the scale represents a two - fold difference in hydrogen ion concentration. b. the lower the whole number on the scale, the greater the h⁺ concentration. c. values above 7 are acidic. d. a substance of ph 2 is more basic than a substance of ph 4.

Explanation:

1. Carbon, hydrogen, oxygen, and nitrogen account for more than 90% of the human body by weight.
2. The reaction $H_2O \to H^+ + OH^-$ is a decomposition reaction as a single compound (water) breaks down into two simpler substances (hydrogen ion and hydroxide ion).
3. Electrolytes are compounds that ionize in water, releasing ions that can conduct electricity.
4. Water is the most abundant inorganic substance in the body.
5. On the pH scale, the lower the whole - number value, the greater the hydrogen ion ($H^+$) concentration. Each whole number represents a ten - fold difference in hydrogen ion concentration, values above 7 are basic, and a substance of pH 2 is more acidic than a substance of pH 4.

Answer:

1. A. Carbon, hydrogen, oxygen, nitrogen
2. A. Decomposition reaction
3. B. Compounds that ionize in water
4. B. Water
5. B. The lower the whole number on the scale, the greater the $H^+$ concentration