Mutualism is an association between individuals of two species, both of which are benefitted but cannot live separately under natural conditions e.g. instances of mutualism exist between animals and plants and also in between plants e.g. lichens.

•Ammensalism is an interaction in which one species causes harm to another spices with its toxic secretion often without gaining any benefit from the interaction.

•Commensalism is the relationship between individuals of two species of which one is benefitted and the other is almost unaffected ; neither benefitted nor harmed.

Mutualism/Symbiosis:
Mutualism is a type of ecological interaction in which both partners benefit from their association. It is a mutually beneficial relationship that is essential for the survival of both partners involved. Symbiosis is a specific form of mutualism in which the partners live closely together and interact with each other on a long-term basis.

Explanation:
In a mutualistic relationship, both partners derive benefits that contribute to their survival and reproductive success. These benefits can be in the form of food, shelter, protection, or other essential resources. The partners in a mutualistic association often have complementary needs or abilities, which allow them to provide each other with what they require.

Examples:
Several examples of mutualism can be found in nature:

1. Pollination: Bees and flowers have a mutualistic relationship where bees collect nectar from flowers for food, while unintentionally transferring pollen from one flower to another, aiding in pollination.

2. Nitrogen fixation: Certain bacteria, such as Rhizobium, form mutualistic associations with leguminous plants. The bacteria fix atmospheric nitrogen into a form that can be used by the plants, while the plants provide the bacteria with nutrients.

3. Cleaner fish and host fish: Cleaner fish, such as cleaner wrasses, remove parasites and dead skin from host fish, benefiting from the food source, while the host fish receive cleaning services and decreased parasite load.

Significance:
Mutualism is crucial for the survival of both partners involved in the association. It allows for the efficient utilization of resources and enhances the fitness and reproductive success of the individuals. Mutualistic interactions can also contribute to the stability and functioning of ecosystems by promoting species diversity and ecological balance.

Alternative Options:
The other options given in the question are not correct:

- Commensalism: In commensalism, one partner benefits while the other is unaffected. It does not involve a mutually beneficial association.
- Amensalism: Amensalism is a type of interaction where one partner is harmed, while the other is unaffected. It does not involve a mutually beneficial association.
- Both A and B: This option is incorrect as commensalism is not a mutually beneficial association. Only mutualism/symbiosis represents a mutually beneficial association necessary for the survival of both partners.