Questions: Which of the following will result when 1% to 5% agar is added to nutrient broth, boiled, and cooled?

The answer is the second one (B): a solid medium.

Explanation for each option:

• A pure culture: This refers to a culture that contains only one type of microorganism. Adding agar to nutrient broth does not inherently result in a pure culture; it depends on the inoculation process.

• A solid medium: When agar is added to nutrient broth and then boiled and cooled, it solidifies, creating a solid medium. Agar is a gelling agent that, when cooled, forms a gel-like structure, making the medium solid.

• A liquid medium: A liquid medium is typically just nutrient broth without agar. Adding agar and cooling it results in a solid medium, not a liquid one.

• A contaminated medium: Contamination refers to the presence of unwanted microorganisms. The addition of agar does not cause contamination; contamination depends on the sterility of the process.

• A mixed culture: A mixed culture contains more than one type of microorganism. The addition of agar does not determine whether the culture is mixed; it depends on the inoculation process.

In summary, adding 1% to 5% agar to nutrient broth, boiling, and cooling it results in a solid medium.