Step 1: Total number of arrangements.
The total number of ways to arrange 5 captains is \( 5! \). Thus, the total arrangements are:
\[
5! = 120
\]
Step 2: Favorable arrangements.
Now, treat the captains of India and Australia as a block. This reduces the problem to arranging 4 blocks (the India-Australia block and the other 3 captains). The number of ways to arrange these 4 blocks is \( 4! \), and since India and Australia can be arranged within their block in \( 2! \) ways, the total favorable arrangements are:
\[
4! \times 2! = 24 \times 2 = 48
\]
Step 3: Probability.
The probability that India and Australia stand next to each other is the ratio of favorable arrangements to total arrangements:
\[
P = \frac{48}{120} = \frac{2}{5}
\]
Thus, the correct answer is \( \frac{2}{5} \), corresponding to option (b).