Symbiosis describes close<span> interactions between two or more different species. There are four main types of symbiotic relationships: mutualism, commensalism, parasitism and competition.</span>
<u>Answer:</u> Electrons are taken up by
and they are lost by 
<u>Explanation:</u>
Redox reaction is defined as the reaction in which oxidation and reduction take place simultaneously. It is also called the reaction where the exchange of electrons takes place.
An oxidation reaction is defined as the reaction in which a chemical species loses electrons takes place. In this reaction, the oxidation state of a substance gets increased.
A reduction reaction is defined as the reaction in which a chemical species gains electrons takes place. In this reaction, the oxidation state of a substance gets reduced.
For the given chemical reaction:

The half-reactions for this redox rection follows:
<u>Oxidation half-reaction:</u> 
<u>Reduction half-reaction:</u> 
Hence, electrons are taken up by
and they are lost by 
The correct answer is A MODEL OF MOUNTAIN FORMATION.
A model refers to a representation of an idea, a process or a system, which is used to explain a specific phenomenon that can not be experienced directly. Models are often used in science to explain many phenomenon. When we are talking about a suitable model to represent an event that happens slowly, the most obvious choice from the options given above is mountain formation. This is because, the process of mountain formation occurs very slowly over a long period of time.