The number 1 is classified as a natural number (or counting number), a whole number, an integer, a rational number, and a real number.

• Natural number: 1 is part of the positive integers used for counting (e.g., 1, 2, 3, ...).
• Whole number: 1 is included in whole numbers, which are natural numbers plus zero.
• Integer: 1 is an integer because it is a whole number without any fractional or decimal part.
• Rational number: 1 is rational because it can be expressed as a fraction (1/1).
• Real number: 1 is a real number as it lies on the number line and represents a quantity.

Thus, 1 fits into multiple standard number classifications reflecting its role in mathematics.