Which rays can be used to read very old written documents?

Correct answer: (d) IR rays

Explanation

Infrared (IR) rays are used to read old documents and manuscripts whose writing has faded, been charred or been written over. Many inks, especially carbon-based ones, absorb infrared light differently from the paper or parchment, so infrared photography (infrared reflectography) makes the hidden text stand out.

X-rays and gamma rays pass through such material and can damage it, and β-rays (fast electrons) are not used for reading.