Questions: 19. The number of determines the identity of an element. A) electrons B) protons C) neutrons D) neutrons plus protons E) protons plus electrons 20. Which of the following is a chemical change? A) Water condenses on a mirror. B) A damp towel dries. C) Peanuts are crushed. D) A "tin" can rusts. E) At least two of the above (a-d) exhibit a chemical change. 21. How many of the following are pure substances? (Check all that apply.) A) water B) air C) carbon D) brass E) gold F) ammonia

19. The number of determines the identity of an element.
A) electrons
B) protons
C) neutrons
D) neutrons plus protons
E) protons plus electrons
20. Which of the following is a chemical change?
A) Water condenses on a mirror.
B) A damp towel dries.
C) Peanuts are crushed.
D) A "tin" can rusts.
E) At least two of the above (a-d) exhibit a chemical change.
21. How many of the following are pure substances? (Check all that apply.)
A) water
B) air
C) carbon
D) brass
E) gold
F) ammonia

Transcript text: 19. The number of $\qquad$ determines the identity of an element. A) electrons B) protons C) neutrons D) neutrons plus protons E) protons plus electrons 20. Which of the following is a chemical change? A) Water condenses on a mirror. B) A damp towel dries. C) Peanuts are crushed. D) A "tin" can rusts. E) At least two of the above (a-d) exhibit a chemical change. 21. How many of the following are pure substances? (Check all that apply.) A) water B) air C) carbon D) brass E) gold F) ammonia

Solution

Solution Steps

Step 1: Determine the Identity of an Element

The identity of an element is determined by the number of protons in its nucleus. This is because the number of protons, also known as the atomic number, is unique to each element. Therefore, the correct answer is B) protons.

Step 2: Identify a Chemical Change

A chemical change involves a substance being transformed into a different substance with different properties. Among the options, rusting of a "tin" can is a chemical change because it involves the formation of a new substance (iron oxide) through a chemical reaction with oxygen. Therefore, the correct answer is D) A "tin" can rusts.

Step 3: Identify Pure Substances

A pure substance is a material with a constant composition and distinct chemical properties. Among the options:
- A) Water is a pure substance (compound).
- B) Air is a mixture, not a pure substance.
- C) Carbon is a pure substance (element).
- D) Brass is an alloy, not a pure substance.
- E) Gold is a pure substance (element).
- F) Ammonia is a pure substance (compound).
Therefore, the pure substances are A) water, C) carbon, E) gold, and F) ammonia.