Step 1: Total Investment and Revenue Breakdown
Let the total amount paid by both Mani and Dinesh be \( 2x \) and \( 3x \) respectively.
Both invested equally and Mani invested 3 lakh. So,
\[
2x + 3x = 3,00,000 \, \quad x = 3.
\]
Thus, initial amounts paid by Mani and Dinesh are:
\[
\text{Mani} = 6,00,000 \,, \quad \text{Dinesh} = 9,00,000 \,.
\]
Hence, total initial investment by Mani and Dinesh together is:
\[
6,00,000 \, + 9,00,000 \, = 18,00,000 \,.
\]
Step 2: Total Revenue Generation
According to the problem, the total revenue generated is 50% of the total initial amount invested by both Mani and Dinesh, i.e., \( 50% \) of 18 lakh:
\[
\text{Total revenue} = 0.5 \times 18,00,000 \, = 9,00,000 \,.
\]
Step 3: Revenue from Coconut and Lemon Trees
The revenue generated from coconut and lemon trees is in the ratio 5 : 4. Thus, the total revenue of 9 lakh is divided in this ratio:
\[
\text{Revenue from coconut} = \frac{5}{9} \times 9,00,000 \, = 5,00,000 \, \]
\[\quad \text{Revenue from lemon} = \frac{4}{9} \times 9,00,000 \, = 4,00,000 \,.
\]
Step 4: Number of Coconuts Reaped
Each coconut costs Rs.10. Hence, the total number of coconuts reaped is:
\[
\frac{5,00,000 \,}{10} = 50,000.
\]
Thus, the correct answer is (B) 50000.
Final Answer: The correct answer is (B) 50000.