Am having a new range installed In my condo which is 45 years old.
Breaker is 50. Contractor says it is not enough for the stove and he wants to put in a 75.
Is that safe?

What does the stove call for? Voltage and Amps? 75 seems very high.

Seems very high. I've never seen a residential range that required more than a 60A breaker. Most only require a 40.

Also, without verifying that the wire can handle it one should never simply put in a larger breaker.

Agree with ma,
The installation instructions will tell you what you need and what is required.
The instructions are also required to be followed by the electrical code...