In a chemical reaction, the total amount of:

Correct Answer: A

Rationale: The Law of Conservation of Mass states that matter cannot be created or destroyed in a chemical reaction, only rearranged. This principle implies that the total amount of matter before and after a chemical reaction must remain constant, supporting the correct answer choice A. Choice B is incorrect because the total amount of matter does not increase in a chemical reaction; it is conserved. Choice C is incorrect as the total amount of matter does not decrease in a chemical reaction; it is conserved. Choice D is incorrect since the conservation of energy is a different principle and does not directly relate to the total amount of matter in a chemical reaction.

Correct Answer: D

Rationale: A catalyst is a substance that increases the rate of a chemical reaction without being consumed in the process. It remains unchanged after the reaction, which eliminates option B. A catalyst works by lowering the activation energy required for the reaction to occur, which eliminates option C. A catalyst does not create new products in a reaction; it only facilitates the conversion of reactants into products more efficiently. Therefore, option D is NOT a property of a catalyst.

Correct Answer: C

Rationale: When two objects with different masses collide, their total momentum remains the same after the collision according to the law of conservation of momentum if no external forces are acting on them. This means that the momentum of each individual object may change, but the sum of their momenta will remain constant. Choice A is incorrect because the total momentum of the system is conserved. Choice B is incorrect because momentum is conserved in an isolated system. Choice D is incorrect as it implies a violation of the law of conservation of momentum, which states that the total momentum of an isolated system remains constant.

Correct Answer: C

Rationale: In an inelastic collision where two objects stick together after colliding, momentum is conserved. Since the two objects have equal masses and equal initial velocities but opposite directions, their momenta cancel out. Therefore, after the collision, the combined mass will move at the same speed as the initial velocity, but in the direction of one of the objects. Choice A ('Zero') is incorrect because momentum is conserved, and the objects must move after the collision. Choice B ('Half their initial velocity') is incorrect as the final velocity is the same as the initial velocity due to momentum conservation. Choice D ('Twice their initial velocity') is incorrect as the final velocity cannot be twice the initial velocity based on the conservation of momentum principle.

Correct Answer: D

Rationale: A species is defined as a group of organisms that can interbreed and produce fertile offspring, which is a fundamental concept in biology. This ability to interbreed and produce fertile offspring is a key characteristic that distinguishes one species from another. Genus (option A) refers to a taxonomic rank that includes one or more closely related species, not the ability to interbreed. Phylum (option B) and kingdom (option C) are higher taxonomic ranks that encompass a broader range of organisms, not specifically defined by interbreeding and fertile offspring production. Therefore, the correct answer is 'Species.'