Which of the following substances is an acid? (Select all that apply)
A. KOH
B. NaOH
C. HCI
D. H2S
C. HCI
C. HCI is an acid.
To determine which of the substances is an acid, we need to understand the properties of acids. Acids are substances that have a sour taste, turn blue litmus paper red, and can react with metals to produce hydrogen gas.
Let's analyze each substance:
A. KOH: KOH is potassium hydroxide, which is a base, not an acid. Bases have a bitter taste and turn red litmus paper blue.
B. NaOH: NaOH is sodium hydroxide, which is also a base, not an acid.
C. HCl: HCl is hydrochloric acid, a strong acid. It is commonly found in the stomach and is known to have a sour taste, turn blue litmus paper red, and react with metals.
D. H2S: H2S is hydrogen sulfide, which is a colorless gas with a foul odor. It is not an acid.
Therefore, the correct answer is C. HCl, as it is the only substance among the options provided that is an acid.