Which one of the following is the longest Latitude?

Latitudes, also known as parallels, are imaginary circles drawn around the Earth parallel to the Equator [4]. The Equator, designated as 0.0 degree latitude, represents the largest circle among all parallels [3]. This is because the Earth is a geoid that bulges at the center and flattens at the poles. As one moves northward or southward from the Equator toward the poles, the circumference of these latitude circles progressively decreases [3]. While the Equator has the maximum length of approximately 40,075 kilometers, the circles become smaller at higher latitudes like 23.5 degrees and 66.5 degrees, eventually shrinking to a single point at the 90 degree North and South poles [4]. Mathematically, the length of a parallel varies as the cosine of its latitude, making the 0° latitude the longest.

Sources

1. [1] Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 18: Latitudes and Longitudes > 18.3. Comparison: Latitude vs. Longitude > p. 250
2. [4] Certificate Physical and Human Geography , GC Leong (Oxford University press 3rd ed.) > Chapter 2: The Earth's Crust > Longitude > p. 11
3. [3] Certificate Physical and Human Geography , GC Leong (Oxford University press 3rd ed.) > Chapter 2: The Earth's Crust > Latitude > p. 10