# DBT JRF 2022 — Question 101

Exam: DBT JRF 2022 · Section: B · Topic: Bioprocess Engineering › Respiratory Quotient & Gas Analysis · Difficulty: Medium

## Question

If the respiratory quotient (R.Q.) for growing cells is 1.1 and the exit gas analyzer of a bioreactor shows 3% $CO_2$ in the outlet gases; then given normal air as input to the reactor, you expect the outlet $O_2$ concentration to read approximately:

## Options

- **A.** 3.3%
- **B.** 2.7%
- **C.** 18.3%
- **D.** 17.7%

## Answer

Option C

## Explanation

Outlet O₂ percentage from RQ calculation: Given: Respiratory Quotient RQ = CO₂ produced / O₂ consumed = 1.1 Exit CO₂ measured = 3% O₂ consumed: $\text{O}_2\,\text{consumed} = \frac{\text{CO}_2\,\text{produced}}{\text{RQ}} = \frac{3\%}{1.1} \approx 2.73\%$ Inlet air composition: ~21% O₂, ~0.04% CO₂ (approximately) Outlet O₂: $\text{O}_{2,\text{outlet}} = \text{O}_{2,\text{inlet}} - \text{O}_{2,\text{consumed}} \approx 21\% - 2.73\% \approx 18.3\%$ Answer: Outlet O₂ ≈ 18.3%.

Source: https://mypyqbuddy.com/questions/if-the-respiratory-quotient-r-q-for-growing-6a104cd5920734408bc0c774