Learning of the mother tongue by a child is generally assumed to be :

The correct option is Language acquisition.

Here is a step-by-step breakdown of the concept:

1. Understanding Language Acquisition:
Language acquisition refers to the natural, subconscious process through which children pick up their native language (mother tongue). It occurs during early childhood when a child is exposed to language in their immediate environment, such as through interactions with parents, siblings, and caregivers, without any formal instruction or deliberate practice.

2. Distinguishing Acquisition from Learning:
- Language Acquisition: A natural, intuitive process focused on communication. Children do not study grammar rules; instead, they develop an internal, subconscious understanding of the language.
- Language Learning: A conscious, structured process that typically happens in a classroom setting where grammar rules, vocabulary lists, and syntax are explicitly taught (e.g., learning a foreign language in school).

3. Conclusion:
Since a child acquires their first language/mother tongue naturally through exposure and social interaction rather than formal instruction, the process is generally assumed to be Language acquisition.