Which element exists in the free state?
A. C
B. Si
C. Ge
D. Sn

Hint: The element is used in a variety of uses in everyday life. It is present in the tip of pencils, jewellery, as well as in industrial purposes like in machines and also in fuels. It is also the most important element in organic chemistry.

Complete step by step solution:
In our question, we have been given with four elements carbon, silicon, germanium and tin. An element is said to exist in free state if it does not combine with any other element. Rather, free state elements are stable even without combining. But combined state elements are those who exist in the combined form always. If they are meant to exist in a free state, then it would be really unstable. Let's check silicon first. Silicon is definitely not a free state element. We will call it a combined state element as silicon exists as silica as well as silicate. Similarly, germanium and tin are metals that occur in the combined state, in nature. But carbon is an exception here. Carbon is such an element that exists both in free state and combined state. We know that carbon forms oxides, mainly carbon dioxide. For this to happen, carbon combines with oxygen, and the same is the case for carbonates too. On the other hand, carbon also exists in free state as allotropes for example diamond, graphite and fullerene.

Hence, we can say that carbon exists in the free state which gives option A as our answer.

NOTE: Among the allotropes of carbon, diamond has a cubic crystal structure. Graphite is the most stable allotrope and is formed under excess pressure and temperature. Fullerene has a large spherical structure and the atoms are $s{{p}^{2}}$ hybridised.