Luminous intensity, the quantity of visible light that is emitted in unit time per unit solid angle. The unit for the quantity of light flowing from a source in any one second (the luminous power, or luminous flux) is called the lumen. The lumen is evaluated with reference to visual sensation. The sensitivity of the human eye is greatest for light having a wavelength of 555 nanometres (10-9 metre); at this wavelength there are 685 lumens per watt of radiant power, or radiant flux (the luminous efficiency), whereas at other wavelengths the luminous efficiency is less. The unit of luminous intensity is one lumen per steradian, which is the unit of solid angle—there are 4π steradians about a point enclosed by a spherical surface. This unit of luminous intensity is also called the standard candle, or candela, one lumen per steradian.

The secondary fundamental unit in the given options is Luminous intensity.

Luminous intensity is a fundamental physical quantity that is used to describe the amount of light emitted or received by a source. It is a measure of the power of light emitted per unit solid angle in a particular direction.

Here is a detailed explanation of why luminous intensity is the secondary fundamental unit:

1. Length:
Length is a fundamental physical quantity and is considered as the primary fundamental unit. It is used to measure the extent of something along one dimension. It is commonly measured in meters (m) or its multiples or submultiples.

2. Plane angle:
Plane angle is another fundamental physical quantity but not a secondary fundamental unit. It is used to measure the amount of rotation or inclination between two lines or planes. Plane angles are measured in radians (rad) or degrees (°).

3. Time:
Time is also a fundamental physical quantity and is considered as the primary fundamental unit. It is used to measure the duration of events or the intervals between them. Time is commonly measured in seconds (s) or its multiples or submultiples.

4. Luminous intensity:
Luminous intensity is the power of light emitted per unit solid angle in a particular direction. It is a fundamental physical quantity but is considered a secondary fundamental unit. Luminous intensity is measured in candela (cd), which is the base unit for measuring brightness or luminous flux.

In the International System of Units (SI), there are seven base units, including length, mass, time, electric current, temperature, amount of substance, and luminous intensity. These base units are used to derive other units for different physical quantities.

In conclusion, the secondary fundamental unit among the given options is luminous intensity (option B). It is a fundamental physical quantity used to measure the power of light emitted per unit solid angle in a particular direction and is measured in candela (cd).

I think it is plane angle