A student wishes to study the cell structure under a light microscope having 10X eyepiece and 45X objective. He should illuminate the object by which one of the following colours of light so as to get the best possible resolution ?

The resolution of a microscope is inversely proportional to the wavelength of the light used for illumination. This means that shorter wavelengths of light will provide higher resolution. Among the options given, blue light has the shortest wavelength, which would provide the best resolution for studying cell structure under a microscope. Therefore, the correct answer is option (C) Blue. Think of it this way: since blue light has a shorter wavelength compared to yellow, green, or red light, it allows for a higher resolution when used for illumination in microscopy.