Solve the Inequality: Find the Missing Number in 201,235 < □ < 203,100

To solve this problem, follow these steps:

• Step 1: Identify the range within which the missing number must lie. The given range is from $201,235$ to $203,100$.
• Step 2: Assess each multiple-choice option provided to see if it falls within this range.

Let's analyze each choice:

• Choice 1: $201,999$ — Since $201,235 < 201,999 < 203,100$, this number lies within the range.
• Choice 2: $203,999$ — This number is greater than $203,100$ and does not fit within the range.
• Choice 3: $200,999$ — This number is less than $201,235$ and does not fit within the range.
• Choice 4: $201,099$ — This number is less than $201,235$ and does not fit within the range.

Therefore, the correct number that fits within the given constraints is $\mathbf{201,999}$.

Hence, the solution to the problem is: $\Box = 201,999$.