Question

the length of the meridians of longitudes is equal where as in the case of parallels of latitudes it decreases towards the north and south poles give suitable reason

Answer 1

This is simple spherical geometry.

Meridians completely encircle the globe, always passing through both poles, and always the full cercumference of the Earth. The only variation is because the Earth is not quite a perfect sphere. But it nearly is, and the variation is very little.

Parallels are quite different - they are all “parallel” to the equator. It is similar to a cone - the higher you go up the cone, the smaller a circle around it will be. This was done mainly because it is pretty easy to determine latitude - there are eight ways I know of - and I can make a primitive Astrolabe (which only measures latitude) using a block of wood (with a notch in it) and a piece of string. While I don’t learn the actual latitude, I can learn the relative one. So I can tell if we have sailed parallel, or gone North or South of where we were last time. That permits me to correct. If I stay on course East or West, I must hit the major North South Coast nearest to me (the Americas, or Africa-Europe- or Asia/SE Asia/Indonesia/Australia. Many methods permit determining the actual latitude. Longitude is hard, and requires good star charts and an accurate clock (called a chronometer).