The partial pressures (in mmHg) of oxygen (O2) and carbon dioxide (CO2) at alveoli (the site of diffusion) are:

(A)pO2 = 104 and pCO2 = 40
(B)pO2 = 40 and pCO2 = 45
(C)pO2 = 95 and pCO2 = 40
(D)pO2 = 159 and pCO2 = 0.3

The NCERT line that answers it

Verbatim line

Inside the alveolus, the partial pressures are $pO_2 = 104 \text{ mmHg}$ and $pCO_2 = 40 \text{ mmHg}$ .

Chapter: Breathing and Exchange of Gases
Section: 14.3 EXCHANGE OF GASES

The answer appears as a continuous sentence in NCERT. This is that sentence.

How this line gives the answer

0, emb=1.0, combined=1.0). Verified: high — The span explicitly states the exact partial pressure values (pO2 = 104 mmHg and pCO2 = 40 mmHg) that match option A, directly answering the MCQ.

We did this for 1,565 questions.

Every one traced to the exact sentence in NCERT that answers it, including 90% of the 2026 paper. Sit a mock on the real NEET 2027 computer interface and every mark you drop comes back with its line attached.

Take the free 5-minute check More from this chapter

Question text is reproduced from the published NEET 2021 paper for study and commentary. NCERT text is quoted, not redistributed; textbooks remain at ncert.nic.in. Our mapping method, including its measured error rates, is published at /methodology.