Filaments of fungi, which have thread-like appearance are called

The correct option is Hyphae.

Fungi are eukaryotic organisms that can exist as single-celled yeasts or multicellular filamentous structures. The vegetative body of a multicellular fungus is known as a mycelium, which is made up of a network of long, thread-like, branching structures.
Each individual thread-like filament is called a hypha (plural: hyphae). These structures play a critical role in the fungus's growth, nutrient absorption, and environmental interaction by secreting enzymes to break down organic matter.

Let us examine why the other options are incorrect:
1. Conidia: These are non-motile, asexual spores formed at the tips of specialized hyphae, not the filaments themselves.
2. Sporangium: This is an enclosure or capsule in which spores are formed and stored.
3. Mycorrhiza: This refers to a symbiotic association between a fungus and the roots of a vascular plant, rather than an individual fungal filament.