Chlorine, bromine and iodine make a Dobereiner's triad. The average of atomic masses of chlorine and Iodine would be close to ______.
- AOption (a)
131.25
- BOption (b)
162.5
- COption (c)
79.9
- DOption (d)
94
View answer & explanationHide answer & explanation
Correct answer
79.9
Why this answer is correct
The correct answer is 79.9.
Key Points
- The Dobereiner's triad is a group of three elements with similar properties.
- In this case, the triad consists of chlorine, bromine, and iodine.
- According to Dobereiner's law of triads, the atomic mass of the middle element is the average of the atomic masses of the other two.
- Therefore, the atomic mass of bromine should be close to the average of the atomic masses of chlorine and iodine.
- The atomic mass of chlorine is 35.5 and the atomic mass of iodine is 126.9.
- Therefore, the average of these two values is (35.5 + 126.9) / 2 = 81.2.
- This value is closest to option 3, which is 79.9.
- Chlorine, bromine, and iodine are halogens, which are highly reactive nonmetals.
- They all have seven valence electrons and tend to form salts with metals.
Additional Information
- Chlorine has an atomic number of 17 and the symbol Cl.
- Among the halogens, it is the second-lightest.
- Atomic number 35 and symbol Br belong to bromine.
- When it is at room temperature, it is a volatile reddish-brown liquid.
- Iodine has an atomic number of 53 and the symbol I.
- Of the stable halogens, it is the heaviest.
- With valence shell d orbitals, chlorine, bromine, and iodine can expand their valence shells to include up to 14 valence electrons.





