Why resistor is used at the output of OPAMP?
R10 definitely looks like an out-of-the-loop compensation to mitigate the influence of capacitive load to U1B (to reduce oscillations, as Indraneel mentionned in comments to the question). See Practical Techniques to Avoid Instability Due to Capacitive Loading, scroll down to "Out-of-the-Loop Compensation". Values of up to 50–100 Ohms are typical.

I hesitate to explain R5 in the same way, though. Its value is on the high side for that purpose, but still plausible. But I don't see from which capacitive load it can isolate U1A, except for the U1D's non-inverting input, which should not be a problem anyway.