The formula of a compound is `A_(2)B_(5).` The number of electrons in the outermst shells of A and B respectively are:

Options

A. 6 and 3
B. 5 and 6
C. 5 and 2
D. 2 and 3.

Answer

To solve the problem regarding the compound with the formula \( A_2B_5 \), we need to determine the number of electrons in the outermost shells of elements A and B. Here's the step-by-step solution:

### Step 1: Understand the Compound Formula
The formula \( A_2B_5 \) indicates that there are 2 atoms of element A and 5 atoms of element B in the compound.

### Step 2: Determine the Valence of A and B
Using the criss-cross method, we can deduce the valence of A and B:
- The subscript of B (which is 5) indicates that the valence of A is +5.
- The subscript of A (which is 2) indicates that the valence of B is -2.

### Step 3: Determine the Number of Electrons in the Outermost Shell
1. **For element A:**
- A has a valence of +5, which means it loses 5 electrons. Therefore, the number of electrons in the outermost shell of A is **5**.

2. **For element B:**
- B has a valence of -2, which means it gains 2 electrons to complete its octet. For B to have a valence of -2, it must have 6 electrons in its outermost shell (since gaining 2 electrons will give it a total of 8, which is a stable octet). Therefore, the number of electrons in the outermost shell of B is **6**.

### Step 4: Final Answer
The number of electrons in the outermost shells of A and B are:
- A: 5 electrons
- B: 6 electrons

Thus, the answer is **5 and 6**.

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