Nokea
At very high temperatures, which state of matter is most commonly present?
- A. Solid
- B. Liquid
- C. Gas
- D. None of the above
Correct Answer: C
Rationale: At very high temperatures, substances tend to exist in the gaseous state. This is because the high energy levels cause the particles to move more rapidly and break free from the solid or liquid state. The increased movement and energy lead to gases being commonly present at very high temperatures. Therefore, the correct answer is 'Gas.'
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What happens to an atom that has a positive charge?
- A. Gained an electron.
- B. Lost an electron.
- C. Gained a proton.
- D. Lost a proton.
Correct Answer: B
Rationale: When an atom has a positive charge, it means it has lost one or more electrons. Electrons carry a negative charge, so the loss of an electron results in the atom becoming positively charged. Therefore, the correct answer is B: Lost an electron.
What is the name for the horizontal rows of the periodic table?
- A. groups
- B. periods
- C. families
- D. sets
Correct Answer: B
Rationale: In the periodic table, the horizontal rows are called 'periods.' These periods represent the number of electron shells an element has. Each period starts a new energy level, indicating the elements' properties and atomic structure. 'Groups' refer to the vertical columns of the periodic table, each containing elements with similar chemical properties. 'Families' can also be used interchangeably with groups. 'Sets' is a vague term and not specifically related to the layout of the periodic table. Understanding the distinction between 'periods' and 'groups' is crucial in comprehending the organization and properties of elements in the periodic table.
What is a combustion reaction?
- A. It is endothermic.
- B. It substitutes one element for another.
- C. It always shares electrons.
- D. It is a reaction that involves oxygen.
Correct Answer: D
Rationale: A combustion reaction is a type of chemical reaction that involves a substance reacting with oxygen gas to produce heat and light. This reaction is exothermic, releasing energy in the form of heat and light. The correct answer is D because combustion reactions specifically involve oxygen as a reactant, leading to the production of heat and light as byproducts.
What is present in an emulsion?
- A. Water and salt
- B. Two or more immiscible liquids
- C. Any liquids
- D. All of the above
Correct Answer: B
Rationale: In an emulsion, two or more immiscible liquids are present. Immiscible liquids are those that do not mix together and form separate layers, such as oil and water. Emulsions are a type of colloid where one liquid is dispersed in another. Water and oil are a common example of an emulsion, where the two liquids do not mix naturally but can be forced to form a stable mixture with the help of an emulsifying agent.
Which type of reaction is exemplified by the chemical equation Cr + Fe(NOÄ‚�)Ä‚‚ Ć’ Fe + Cr(NOÄ‚�)Ä‚�?
- A. Single replacement
- B. Decomposition
- C. Double replacement
- D. Combustion
Correct Answer: A
Rationale: The given chemical equation represents a single replacement reaction. In this type of reaction, one element displaces another element in a compound. In the provided equation, chromium (Cr) replaces iron (Fe) in the compound Fe(NOÄ‚�)Ä‚‚, resulting in the formation of Fe and Cr(NOÄ‚�)Ä‚�. Single replacement reactions involve the substitution of one element for another in a compound, which is precisely demonstrated in this scenario. Therefore, the correct classification for this reaction is a single replacement reaction.