Step 1: Understanding the Concept:
\textit{Chenna} is fresh, unripened curd cheese made from cow or buffalo milk by curdling it with an edible acid like lemon juice or vinegar. It is the foundation of most Bengali desserts.
Step 2: Detailed Explanation:
Four popular Chenna sweets are:
1. Rasgulla: Spongy balls of chenna cooked in a light sugar syrup. They must be porous and elastic.
2. Sandesh: Made by kneading fresh chenna with sugar or jaggery (Nolen Gur) and often flavored with cardamom or saffron. It is a dry sweet.
3. Rasmalai: Flattened discs of chenna (similar to rasgullas) which are soaked in a thickened, sweetened, and flavored milk known as 'Rabri'.
4. Cham Cham: These are colorful, often oval-shaped chenna sweets that are denser than rasgullas and sometimes coated with desiccated coconut or topped with mawa (khoya).
Step 3: Final Answer:
The sweets are Rasgulla, Sandesh, Rasmalai, and Cham Cham.