​What are the paired organs of balance commonly found in aquatic invertebrates which are usually fluid-filled vesicles with sensory hairs?​

Correct option is A

Statocysts are paired organs of balance found in aquatic invertebrates. They are fluid-filled vesicles that contain sensory hairs called statoliths. These statoliths move within the fluid in response to gravity, stimulating the sensory hairs and providing information about the animal's orientation. This helps the animal maintain balance and coordinate its movements in water.

Incorrect options explanation:

The nephridium (pl. : nephridia) is an invertebrate organ, found in pairs and performing a function similar to the vertebrate kidneys (which originated from the chordate nephridia). Nephridia remove metabolic wastes from an animal's body.

It is a minutely toothed, chitinous ribbon, which is typically used for scraping or cutting food before the food enters the esophagus. The radula is unique to the mollusks, and is found in every class of mollusk except the bivalves, which instead use cilia, waving filaments that bring minute organisms to the mouth.

The pharynx (throat) is a muscular tube in the middle of your neck. It helps you to breathe and digest food. Many medical issues can affect your pharynx, from a common cold to cancer. You can protect your pharynx by not smoking and avoiding infection.