UPSC CAPF AC 2025 Paper 1 · Question 102
Question 102 of the UPSC CAPF (AC) 2025 Paper I (3 August 2025). Try it first, then open the answer and explanation.
Which of the following triads was not given by Dobereiner?
- Ca, Sr, Ba
- Cl, Br, I
- N, P, As
- Be, Mg, Ca
निम्नलिखित में से कौन-सा त्रिक (triad) डॉबेराइनर द्वारा नहीं दिया गया था?
- Ca, Sr, Ba
- Cl, Br, I
- N, P, As
- Be, Mg, Ca
Show answer
Answer: (3) N, P, As
उत्तर: (3) N, P, As
In a Dobereiner triad the atomic mass of the middle element is roughly the mean of the other two; for N, P, As the mean of N (14.0) and As (74.9) is about 44.5, far from P (31.0), so it is not a triad. Ca, Sr, Ba (mean 88.7 vs Sr 87.6) and Cl, Br, I (mean 81.2 vs Br 79.9) are his classic triads, and Be, Mg, Ca also fits the rule (mean 24.5 vs Mg 24.3).