which of the following safety precautions is adequate when working with radation of wavelength less than 250 n

Answer 1

which safety precautions are you considering? You didn't let us know which were an option.

What type of radiation? I assume that if you mention a wavelenth and 250 n (I assume you mean nm), .. you're talking about light?

If this is the case, you need eye protection rated for the specific wavelenth. Check Sigma-Aldrich, Fisher, or Granger or any other lab safety supply company - the personal protective equipment section will specify the parameters for all of the safety glasses/goggles.