A conjoint and open vascular bundle will be observed in the transverse section of
(a) Monocot root
(b) Monocot stem
(c) Dicot root
(d) Dicot stem

Hint: Plants like oaks, roses, mustards, cacti, sunflowers etc. come under conjoint and open vascular bundles in the plant part which helps in transporting the absorbed water and minerals to different parts of the plant.

Complete step by step answer:
In a dicot stem vascular bundle located inner to pericycle which is developed from procambium and is arranged as a broken ring. It is composed of xylem and phloem where xylem is placed inner to cambium and phloem is placed outer to the cambium. In an open vascular bundle, cambium is present between xylem and phloem. Xylem shows secondary growth. The open vascular bundle is open for secondary growth. Cambium present between xylem and phloem is known as fascicular cambium. Dicot vascular bundles are conjoined that is the presence of xylem and phloem together where xylem is endarch that is protoxylem towards the interior, open with cambium and collateral or biocollerteal.

Additional Information:
Dicot stem:
- Epidermis: This is the outermost layer composed of parenchymatous cells which is usually a single layer of cells. These are closely packed cells, with no intercellular spaces. The outer tangential wall is thick and deposited with a fatty substance that is cutin which presents as a separate layer called the cuticle.
- Cortex: This is an inner tissue to the epidermis. In some dicot plants, the cortex is simple and undifferentiated. In the majority of dicot plants, this is composed of four zones that are hypodermis, outer cortex, inner cortex, endodermis.
- Stele: This is the central vascular cylinder which is composed of four components that are pericycle, vascular bundle, medullary rays and pith.
The pericycle is located inner to endodermis which may be completely parenchymatous, completely sclerenchymatous forms bundle cap or a mixture of parenchymatous or sclerenchymatous alternating bands.
Dicot leaf:
- The leaves of the plants have veins that form a branched type pattern, unlike monocots, in which they run parallel.
- The veins are actually netted or webbed present on the whole surface of the leaf.
Dicot seed:
- There are two cotyledons in the seeds of these plants that actually emerge from the soil when the seed germinates.
- They then turn green and form the first two leaves for the new plant.
So, the correct answer is, ‘(d) Dicot stem.’

Note:
Similarities between dicot stem and monocot stem:
- Thick layer of cuticle present in both groups.
- Hypodermis is present in both the groups (cell type varies) .
- Major portions of ground tissue are parenchymatous.
- Vascular bundles are conjoint and collateral in both the groups.
- In monocots and dicots xylem and phloem are composed of both proto‐ that is protoxylem and protophloem and meta‐ elements that are metaxylem and metaphloem.