What part of the visible spectrum has the longest wavelength? 2. What is the formula for the power of a lens?

1)
The visible spectrum consists of colors ranging from Red to Violet. Red light has the longest wavelength, while violet light has the shortest wavelength. The order of colors from longest to shortest wavelength is Red, Orange, Yellow, Green, Blue, Indigo, Violet (ROYGBIV).

The correct option is A.

$$\boxed{\text{A. Red}}$$

2)
The power of a lens ($P$) in diopters is defined as the reciprocal of its focal length ($f$) in meters.

$$P = \frac{1}{f}$$

The options provided (3f, 2f, f) are not standard expressions for the power of a lens if 'f' represents the focal length