`A + B rarr C + D`
For this reaction 13 gm eq of B is taken which is the reagent in excess. The left over ‘B’ after this reaction required 5 gm eq of a reagent to react completely. Calculate the number of gram equivalents of A in reaction.

Options

A. 13
B. 8
C. 5
D. 18

Explanation

To solve the problem step by step, we will analyze the given information and apply stoichiometric principles.

### Step 1: Understand the Reaction
The reaction is given as:
\[ A + B \rightarrow C + D \]

### Step 2: Identify the Given Information
- We have 13 gram equivalents of B initially.
- B is in excess, meaning that not all of B will react.
- After the reaction, there are 5 gram equivalents of B left over.

### Step 3: Calculate the Amount of B that Reacted
To find out how much B reacted, we subtract the leftover B from the initial amount:
\[ \text{Reacted B} = \text{Initial B} - \text{Leftover B} \]
\[ \text{Reacted B} = 13 \, \text{gm eq} - 5 \, \text{gm eq} = 8 \, \text{gm eq} \]

### Step 4: Relate the Amount of A that Reacted
From the balanced reaction, we see that 1 gram equivalent of A reacts with 1 gram equivalent of B. Therefore, if 8 gram equivalents of B reacted, then:
\[ \text{Reacted A} = \text{Reacted B} = 8 \, \text{gm eq} \]

### Conclusion
The number of gram equivalents of A that reacted is:
\[ \text{A} = 8 \, \text{gm eq} \]

### Final Answer
The number of gram equivalents of A in the reaction is **8 gram equivalents**.

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