JEE Chemistry 2024 Question with Solution

Given: The ions are $\mathrm{Sr}^{2+}$, $\mathrm{Ba}^{2+}$, $\mathrm{Ca}^{2+}$, $\mathrm{Cu}^{2+}$, $\mathrm{Zn}^{2+}$, $\mathrm{Co}^{2+}$ and $\mathrm{Fe}^{2+}$.

Find: The number of metal ions that can be characterized by the flame test.

The flame test identifies metal ions that impart a distinct characteristic colour to the flame.

From the given analysis:

• $\mathrm{Sr}^{2+}$ gives a bright red or crimson red flame.
• $\mathrm{Ba}^{2+}$ gives a green or apple green flame.
• $\mathrm{Ca}^{2+}$ gives an orange-red or brick red flame.
• $\mathrm{Cu}^{2+}$ gives a blue-green flame.
• $\mathrm{Zn}^{2+}$ does not give a useful characteristic flame colour.
• $\mathrm{Co}^{2+}$ does not give a useful characteristic flame colour.
• $\mathrm{Fe}^{2+}$ does not give a useful characteristic flame colour for identification.

So, the ions characterized by flame test are $\mathrm{Sr}^{2+}$, $\mathrm{Ba}^{2+}$, $\mathrm{Ca}^{2+}$ and $\mathrm{Cu}^{2+}$.

Hence, the total number is $4$.

Therefore, the correct option is B.

Given: A list of seven metal ions is provided.

Find: How many among them show characteristic flame colours.

Check each ion one by one:

1. $\mathrm{Sr}^{2+}$ → characteristic flame colour present.
2. $\mathrm{Ba}^{2+}$ → characteristic flame colour present.
3. $\mathrm{Ca}^{2+}$ → characteristic flame colour present.
4. $\mathrm{Cu}^{2+}$ → characteristic flame colour present.
5. $\mathrm{Zn}^{2+}$ → no useful characteristic flame colour.
6. $\mathrm{Co}^{2+}$ → no useful characteristic flame colour.
7. $\mathrm{Fe}^{2+}$ → no useful characteristic flame colour.

Thus, the count of ions identified by flame test is

Therefore, the correct option is B.