The electron affinity of a hypothetical element `'A'` is `3eV` per atom. How much energy in kcal is released when `10g` of `'A'` is completely converted of `A^(-)` ion in a gaseous state ?
`(1 eV=23" kcal mol"^(-1)`, Molar mass of `A=30g)`

Explanation

To find the energy released when 10 grams of the hypothetical element 'A' is completely converted to A^(-) ions in a gaseous state, we can follow these steps:

### Step 1: Understand the Electron Affinity
The electron affinity of element 'A' is given as 3 eV per atom. This means that when one atom of 'A' gains an electron, it releases 3 eV of energy.

### Step 2: Convert Electron Affinity to Kilocalories
We know that 1 eV is equivalent to 23 kcal/mol. Therefore, the energy released per atom in kilocalories can be calculated as:
\[ \text{Energy per atom} = 3 \, \text{eV} \times 23 \, \text{kcal/mol} = 69 \, \text{kcal/mol} \]

### Step 3: Calculate Moles of 'A' in 10 grams
The molar mass of 'A' is given as 30 g/mol. To find the number of moles in 10 grams of 'A', we use the formula:
\[ \text{Number of moles} = \frac{\text{mass (g)}}{\text{molar mass (g/mol)}} = \frac{10 \, \text{g}}{30 \, \text{g/mol}} = \frac{1}{3} \, \text{mol} \]

### Step 4: Calculate Total Energy Released
Now, we can calculate the total energy released when 10 grams of 'A' is converted to A^(-) ions. Since we have \(\frac{1}{3}\) mol of 'A', the total energy released is:
\[ \text{Total energy} = \text{Energy per mole} \times \text{Number of moles} = 69 \, \text{kcal/mol} \times \frac{1}{3} \, \text{mol} = 23 \, \text{kcal} \]

### Final Answer
The total energy released when 10 grams of 'A' is completely converted to A^(-) ions in a gaseous state is **23 kcal**.

---