Stroma is the ground material of which of these

The correct option/answer is Chloroplasts.

Let's break down the explanation step-by-step to understand why this is the correct answer:

1. Understanding Chloroplast Structure: Chloroplasts are double-membraned organelles found in plant cells and algae, responsible for conducting photosynthesis.

2. Defining the Stroma: Inside the inner membrane of a chloroplast, there is a gel-like fluid or ground substance called the stroma. This fluid surrounds the thylakoids (grana), which are the site of the light-dependent reactions of photosynthesis.

3. Role of the Stroma: The stroma contains enzymes necessary for the light-independent reactions (Calvin cycle), which convert carbon dioxide into carbohydrates. It also houses the chloroplast's own DNA, ribosomes, and RNA, enabling protein synthesis within the organelle.

4. Comparing with other options:
- Ribosomes: These are tiny ribonucleoprotein complexes without membranes, not containing a stroma.
- Lysosomes: These are membrane-bound sacs containing digestive (hydrolytic) enzymes, and their internal fluid is not referred to as stroma.
- Mitochondria: The ground fluid inside the inner membrane of a mitochondrion is called the matrix, not the stroma.

Therefore, stroma is the ground material of Chloroplasts.