Step 1: Fractions of the total:
Find what fraction of the Rs. 12 lakh profit each person kept.
Ankit: $\frac{6}{12} = \frac{1}{2}$.
Ashish: $\frac{3}{12} = \frac{1}{4}$.
Arun: $\frac{3}{12} = \frac{1}{4}$.
Step 2: Bring to a common denominator:
The three fractions are $\frac{1}{2}, \frac{1}{4}, \frac{1}{4}$. Write $\frac{1}{2}$ as $\frac{2}{4}$. Now all three have the denominator 4.
The shares are $\frac{2}{4}, \frac{1}{4}, \frac{1}{4}$.
Step 3: Read off the ratio:
When the denominators are equal, the ratio of the fractions is the ratio of the numerators.
\[ 2 : 1 : 1 \]
Step 4: Match with the options:
Only option (2) shows 2:1:1. In the other options the first term is 3 or 4 times some other term, or the last two terms differ, which cannot happen because Ashish and Arun kept the same amount.
Final Answer:
Ankit's share is double each of the other two equal shares, so the ratio is 2:1:1.
\[ \boxed{2:1:1} \]