Which of the following statement(s) is/are true? (i). Flame photometry is good only for elements that are easily excited and do not require very high temperatures (ii). Na, K, Li and Ca are the most widely determined atoms by this technique
- AOnly (i)
- BOnly (ii)
- CBoth (i) and (ii)Correct
- DNeither (i) nor (ii)
Solution
Concept
Flame photometry measures light emitted by atoms excited in a flame. It works well for alkali and alkaline earth metals.
Step-by-step solution
1. In flame photometry, the sample is sprayed into a flame. 2. Easily excited atoms emit light of a fixed wavelength. The flame temperature is low (about 1800–2200 °C). 3. Metals like Na, K, Li and Ca are easily excited. So they are the most commonly measured. 4. Statement (i) is true. Statement (ii) is true.
Explanation
Flame temperature is low, so only easily excited elements give a good signal. Na, K, Li and Ca are the usual elements measured. So both statements are true.
Why the other options are wrong
A: (ii) is also true. B: (i) is also true. D: Both statements are true.
Shortcut
Flame photometer = Na, K, Li, Ca (alkali and alkaline earth metals).
Common mistake
Thinking flame photometry can measure heavy metals. These need AAS or ICP.
Correct answer: C) Both (i) and (ii)