how many neutrons are in an atom of uranium 235

HESI A2

Chemistry HESI A2 Practice Test

1. How many neutrons are in an atom of uranium-235?

A. 92
B. 125
C. 143
D. 235

Correct answer: A

Rationale: The correct answer is A: '92'. To determine the number of neutrons in an atom, you subtract the atomic number (number of protons) from the atomic mass number. For uranium-235, the atomic number is 92, and the atomic mass number is 235. Subtracting 92 from 235 gives us 143 neutrons in an atom of uranium-235. Therefore, options B, C, and D are incorrect as they do not represent the correct number of neutrons in an atom of uranium-235.

2. What charge do alpha radiation particles have?

A. -2
B. 0
C. +2
D. +1

Correct answer: C

Rationale: The correct answer is C: +2. Alpha radiation particles consist of two protons and two neutrons, giving them a net charge of +2. This positive charge is due to the presence of the two protons in the nucleus of the alpha particle. Choice A (-2) is incorrect as alpha particles have a positive charge. Choice B (0) is incorrect as alpha particles carry a charge. Choice D (+1) is incorrect as alpha particles have a higher positive charge due to the presence of two protons.

3. What is the primary function of enzymes?

A. To provide energy for reactions
B. To speed up reactions
C. To decrease activation energy
D. To act as a catalyst

Correct answer: B

Rationale: Enzymes function to speed up reactions by lowering the activation energy required for the reaction to occur. They act as biological catalysts, providing an alternative pathway for the reaction to proceed more rapidly without being consumed in the process. Choices A, C, and D are incorrect because enzymes do not provide energy for reactions (they do not generate energy), their primary function is not to decrease activation energy (though they do lower it), and while they act as catalysts, the primary function is to speed up reactions by lowering activation energy.

4. If oxygen is in a compound, what would its oxidation number be?

A. 2
B. -2
C. 0
D. -1

Correct answer: B

Rationale: Oxygen typically has an oxidation number of -2 in compounds because it tends to gain electrons. This is due to its high electronegativity, which leads to oxygen attracting electrons towards itself in a chemical bond. Choice A (2) is incorrect because oxygen doesn't have a +2 oxidation number in compounds. Choice C (0) is incorrect as oxygen rarely has an oxidation number of 0 in compounds. Choice D (-1) is incorrect as oxygen's oxidation number in compounds is typically -2, not -1.

5. What is the correct formula for silver hydroxide?

A. AgO
B. AgOH
C. AgH
D. AgHâ‚‚O

Correct answer: B

Rationale: The correct formula for silver hydroxide is AgOH. Silver hydroxide is formed by the combination of the silver ion (Agâº) with the hydroxide ion (OHâ») to create AgOH. It is essential to note that the hydroxide ion consists of one oxygen and one hydrogen atom, thus the formula AgOH. Choices A, C, and D are incorrect as they do not accurately represent the composition of silver hydroxide.