A pixel is:

The correct answer is The smallest resolvable part of a picture.

• Explanation: A pixel, short for 'picture element', is the smallest individual unit of a digital image or display that can be controlled or represented. Each pixel contains color information, and when many pixels are combined, they form a complete image. The resolution of an image or screen is determined by the number of pixels it contains.
• Why other options are false:
• B (A picture stored in secondary memory): A pixel is a component of a picture, not the entire picture itself, nor does it describe where the picture is stored.
• C (A computer program that draws picture): A pixel is a data unit, a building block of an image, not a program or software.
• D (A virus): A pixel is a fundamental concept in digital imaging and has no relation to computer viruses.