Correct Answer: B

Rationale:
To prepare a 0.100 M HCl solution with a volume of 500 mL, you can use the formula C1V1 = C2V2, where C1 is the concentration of the concentrated HCl solution, V1 is the volume of concentrated HCl solution used, C2 is the desired concentration (0.100 M), and V2 is the final volume (500 mL). Rearranging the formula to solve for V1, you get V1 = (C2V2) / C1. Plugging in the values (0.100 M)(500 mL) / C1 = 100 mL, which means 100 mL of concentrated HCl should be used to prepare 500 mL of a 0.100 M HCl solution.
Therefore, the correct answer is 100 mL.
Choice A (75 mL),
Choice C (125 mL), and
Choice D (150 mL) are incorrect as they do not match the calculated volume needed to prepare the desired concentration of HCl solution.

Correct Answer: B

Rationale: The correct answer is 'Acid.' An acid is a compound that donates protons (H+), is corrosive to metals, and turns blue litmus paper red. When an acid is mixed with a base, they react to form salts and water, resulting in a decrease in acidity.

Choices A, C, and D are incorrect because bases accept protons rather than donate them, salts are the products of acid-base reactions, and hydroxides are typically bases, not acids.

Correct Answer: C

Rationale: Tap water typically falls within the pH range of 6 to 8, making it slightly acidic to neutral. Most municipal water systems aim to provide water that is safe for consumption and falls within this pH range. A pH level of 7 is considered neutral, so tap water may vary slightly on either side of this number but typically remains within the 6 to 8 range to ensure it is safe for consumption.

Choices A, B, and D are incorrect because tap water is not expected to have a pH as low as 1-3 (highly acidic) or as high as 8-10 (alkaline); it usually falls within the slightly acidic to neutral range, hence falling between 6 and 8 on the pH scale.

Correct Answer: B

Rationale: Potassium, with the atomic symbol K, has 19 protons, which is equal to its atomic number. The number of protons determines the element's identity, and in the case of Potassium, it is 19.
Choice A (18) is incorrect as it does not correspond to Potassium's proton number.
Choice C (20) and
Choice D (21) are also incorrect as they do not match the actual number of protons in Potassium.

Correct Answer: C

Rationale: In the presence of an acid, phenolphthalein turns pink. Phenolphthalein is a pH indicator that is colorless in acidic solutions but turns pink in basic solutions.
Therefore, when added to an acidic solution, phenolphthalein will exhibit a pink coloration.
Choice A, 'Clear,' is incorrect because phenolphthalein does not remain colorless in the presence of an acid.
Choice B, 'Blue,' is incorrect as phenolphthalein does not turn blue in the presence of an acid.
Choice D, 'Red,' is incorrect as phenolphthalein does not exhibit a red color in acidic solutions.