TEAS 7 science practice

Correct Answer: C

Rationale: The correct answer is C: Double helix. The shape of the DNA molecule is a double helix, a structure first described by James Watson and Francis Crick in 1953. This shape consists of two strands twisted around each other in a spiral. The double helix structure allows DNA to be compactly stored within the cell nucleus and provides stability to the molecule. Options (A) Linear, (B) Circular, and (D) Straight chain are incorrect as they do not accurately represent the shape of the DNA molecule. DNA is not linear but rather forms a twisted double helix; it is not circular like a ring but has a spiral structure, and it is not a straight chain but a twisted ladder-like structure.

Correct Answer: A

Rationale: The speed of a wave in a given medium is determined by the product of its frequency and wavelength. This relationship is described by the formula: Speed = Frequency Wavelength. When a wave travels through a medium, the speed at which it propagates is directly proportional to both its frequency and wavelength. Therefore, to calculate the speed of the wave, you multiply the frequency of the wave by its wavelength. Choices B, C, and D are incorrect because speed is not determined by division, addition, or subtraction of frequency and wavelength; instead, it is determined by their multiplication in the given medium.

Correct Answer: D

Rationale: The van't Hoff factor (i) represents the number of particles a solute dissociates into in solution. For a compound that dissociates completely in water, i would be more than 1 because it breaks apart into more particles than the original compound. This is due to complete dissociation leading to an increase in the number of particles in solution, resulting in i being greater than 1. Choice A is incorrect as a compound that dissociates completely will not have an i value of 0. Choice B is incorrect because when a compound dissociates completely, the van't Hoff factor is not less than 1. Choice C is incorrect as a compound that dissociates completely will not have an i value of 1, but rather more than 1 due to the increased number of particles in solution.

Correct Answer: B

Rationale: The correct answer is increasing pressure. According to Henry's Law, the solubility of a gas in a liquid is directly proportional to the partial pressure of the gas above the liquid. Therefore, increasing pressure would force more gas molecules into the liquid, leading to an increase in solubility. Conversely, decreasing temperature, decreasing surface area, and increasing particle size would not directly impact the solubility of a gas in a liquid. Decreasing temperature typically decreases solubility as gases are less soluble at lower temperatures. Decreasing surface area and increasing particle size are related to surface area and not the pressure above the liquid, thus not affecting solubility as pressure does.

Correct Answer: A

Rationale: A saturated hydrocarbon chain contains only single bonds between carbon atoms, making it 'saturated' with hydrogen atoms. Therefore, the correct answer is choice A, 'Saturated.' Choice B, 'Unsaturated,' is incorrect because it refers to hydrocarbon chains with double or triple bonds. Choice C, 'Aromatic,' is not the correct term for a hydrocarbon chain without double or triple bonds; it describes a specific type of cyclic and conjugated hydrocarbon structure. Choice D, 'Alkene,' is also incorrect as it specifically indicates a hydrocarbon chain with at least one double bond between carbon atoms.