Okay, let's see. I need to find out how long the hallway is in meters. The robot's speed is constant, so I can probably use the formula distance equals speed multiplied by time. The problem gives me two different pieces of information: one about the time it takes to travel 1 kilometer and another about the time it takes to go through the hallway. 

First, let me parse the information. The robot takes 2.5 hours to travel 1 kilometer. Wait, 1 kilometer is 1000 meters, right? So if I can find the speed in meters per second, then I can use the time it takes to go through the hallway (which is 90 seconds) to find the distance. 

But the first piece of information is in hours, so maybe I should convert everything to the same units. Let me think. If the robot takes 2.5 hours to go 1 kilometer, I can calculate its speed in kilometers per hour first. Then convert that to meters per second or maybe even kilometers per second. Let me try that.

So speed is distance divided by time. Here, the distance is 1 kilometer, and the time is 2.5 hours. So speed = 1 km / 2.5 hours = 0.4 km/hour. 

Now, to convert this speed to meters per second. Since 1 kilometer is 1000 meters and 1 hour is 3600 seconds, so 0.4 km/hour is 0.4 * 1000 meters / 3600 seconds. Let me calculate that. 

0.4 * 1000 = 400 meters. 400 divided by 3600 seconds. Let's simplify that. 400/3600 = 1/9 meters per second. So the robot's speed is 1/9 m/s. 

Now, the hallway takes 90 seconds to traverse. So the length of the hallway would be speed multiplied by time. So 1/9 m/s * 90 s. Let's compute that. 90 divided by 9 is 10. So the hallway is 10 meters long. 

Wait, that seems straightforward. Let me check if I missed anything. The robot is moving at a constant speed, so the calculation should be correct. Let me verify the steps again.

1. Convert 2.5 hours to time in seconds to see if that's an alternative approach. 2.5 hours is 2.5 * 3600 seconds. 2 * 3600 is 7200, 0.5 * 3600 is 1800, so total 9000 seconds. So 1 km in 9000 seconds. Then speed is 1000 meters / 9000 seconds = 100/900 = 10/90 = 1/9 m/s. Yep, same result. 

Then hallway time is 90 seconds. So 1/9 m/s * 90 s = 10 meters. That checks out. 

Alternatively, using km/hour: 0.4 km/hour is 0.4 km per 60 minutes. 90 seconds is 1.5 minutes. So in 1.5 minutes, how much distance? Since 0.4 km per 60 minutes, per minute it's 0.4/60 km. So 0.4/60 * 1.5 minutes. Let's compute that. 0.4 divided by 60 is 0.006666... per minute. Multiply by 1.5 gives 0.01 km, which is 10 meters. Same answer. 

So all methods lead to 10 meters. Therefore, the hallway is 10 meters long. I think that's correct.
Therefore, the hallway is $\boxed{10}$ meters long.
</think>