# DBT JRF 2020 — Question 34

Exam: DBT JRF 2020 · Section: B · Topic: Biotechnology · Difficulty: Hard

## Question

Which of the following yeast is used for the production of riboflavin?

## Options

- **A.** Saccharomyces rouxii
- **B.** Saccharomyces cerevisiae
- **C.** Candida utilis
- **D.** Eremothecium ashbyi

## Answer

Option D

## Explanation

Acid strength and pKa: $\text{pKa} = -\log_{10}(K_a)$ . A lower pKa = stronger acid (higher $K_a$ ). Ranking from weakest (highest pKa) to strongest (lowest pKa): Acetic acid ( $\text{CH}_3\text{COOH}$ , pKa = 4.75) → weakest. Trifluoroacetic acid (TFA, $\text{CF}_3\text{COOH}$ , pKa ≈ 0.0) → the three electron-withdrawing F atoms stabilise the conjugate base. Sulfuric acid ( $\text{H}_2\text{SO}_4$ , pKa $_2 \approx -3$ , but pKa $_1 = -3$ as well for the first dissociation) → strong acid. Hydrochloric acid (HCl, pKa ≈ -7) → strongest. Order of INCREASING acid strength (decreasing pKa): Acetic acid < TFA < $\text{H}_2\text{SO}_4$ < HCl. In terms of pKa values from high to low: Acetic acid > TFA > $\text{H}_2\text{SO}_4$ > HCl.

Source: https://mypyqbuddy.com/questions/which-of-the-following-yeast-is-used-for-6a05a8a02adafec47029323a