Lichen is usually cited as an example of ‘symbiosis’ in plants where an algal and a fungal species live together for their mutual benefit. Which of the following will happen if algal and fungal partners are separated from
each other?
a. Both will survive and grow normally and independent from each other.
b. Both will die
c. Algal component will survive while the fungal component will die.
d. Fungal component will survive while algal partner will die.

Symbiosis is the term used for the relationship in which two organisms get benefit from each other. 
Lichen is a symbiotic relationship between algae and fungus.But the symbiotic relationship is an obligate one. This means that the organisms require the symbiotic relationship in order to survive.  

The algae and fungus are mutually dependent on each other. The fungus is the only source of water and nutrients for the algae. 
Algae is the only source of food to the fungus. There are no alternative means for meeting the basic needs. Thus, If the two are sperated both will die because they will not be able to fulfil the requirements in the absence of the other.

Thus option b is true. Both will die.