what is the major difference between monocot and dicot stem which we can identify by seeing their diagrams???

Hi

Anatomically, monocot stem can be distinguish from dicot stem by observing the arrangement of vascular bundles.

The vascular bundles in the monocot stems are scattered in the cortex; thus, you will not able to demarcate the pith. In case of dicot stems a large number of vascular bundles are arranged in a ring;  thus, a conspicuous pith in visible. Moreover, the vascular bundles of monocot stem consists of only xylem and phloem while you will be able to see cambium sandwitched between xylem and phloem in dicot stems.

Precisely, if a section of stem has large pith and open vascular bundles arranged in ring fashion then it is a dicot stem. And if the vascular bundles are closed and scattered, and pith is absent then it is a monocot stem.

Cheers!