Step 1: Understanding the Concept:
Identify the square root of the first number and see how it relates to the second number. Step 2: Detailed Explanation:
$121 = 11^2$.
The relationship is $\sqrt{121} + 1 = 11 + 1 = 12$. Step 3: Calculation:
Applying the same logic ($\sqrt{x} + 1$) to 25:
$\sqrt{25} + 1 = 5 + 1 = 6$. Step 4: Final Answer:
The missing number is 6. Thus, the correct option is (c).