The correct answer is option 'C' - Cortex is present.

Explanation:

Monocot stems are one type of plant stems that belong to the monocotyledonous group of plants. Monocotyledonous plants are characterized by having a single cotyledon (embryonic leaf) in their seeds. Monocot stems have some distinct features that differentiate them from dicot stems.

1. Vascular Bundles:
In a monocot stem, the vascular bundles are scattered throughout the ground tissue. These vascular bundles are composed of xylem and phloem tissues, which transport water, minerals, and nutrients throughout the plant. The scattered arrangement of vascular bundles is different from the concentric arrangement found in dicot stems.

2. Conjoint Vascular Bundles:
Contrary to option 'B', monocot stems have only one conjoint vascular bundle. A conjoint vascular bundle consists of both xylem and phloem tissues arranged in a ring-like structure. This vascular bundle is responsible for the transport of water, nutrients, and sugars.

3. Cortex:
Option 'C' states that the cortex is present in a monocot stem, which is incorrect. The cortex is a region of ground tissue present between the epidermis and the vascular bundles. In dicot stems, the cortex is well-developed and plays a role in storage. However, in monocot stems, the cortex is absent or poorly developed. The ground tissue in monocot stems is mainly composed of parenchyma cells.

4. Cambium:
Option 'D' states that cambium is absent in monocot stems, which is correct. Cambium is a meristematic tissue found in the vascular bundles of dicot stems. It is responsible for secondary growth, leading to an increase in stem girth. Monocots do not undergo secondary growth, and therefore, lack a vascular cambium.

In conclusion, the correct statement about the monocot stem is that the cortex is absent (option 'C'). The other options, such as scattered vascular bundles, the presence of one conjoint vascular bundle, and the absence of cambium, are correct features of monocot stems.