How to confirm the presence of carbon in a compound? How does carbon attain a noble gas configuration with a valency of four?

                                                  (OR)

Why does carbon forms more compounds than any other element? Give two reasons.

Confirmation test:

Burn the compound in the presence of air or oxygen, and gas production will occur due to combustion. The presence of $C{O}_2$ confirmed using the Lime water test.

If the lime water turns milky, it indicates the production of $C{O}_2$ gas, thereby confirming the presence of carbon in a compound.
The reaction that occurs when it is added to lime water is as follows:

$Ca\left(O{H}_2\right)+C{O}_2\to CaC{O}_3$.

With a valency of 4, carbon possesses four electrons in its outermost shell. Carbon atoms form covalent bonds by sharing these 4 electrons with other atoms, thus attaining noble gas configuration in its compounds.

                                                   (OR)

The number of carbon compounds is more than those formed by all other elements put together due to the following reasons: 

1) It is due to the carbon's ability to self-link and catenation. 

2) Since carbon has a valency of four, it can bond with four other carbon atoms or atoms of other monovalent elements. 

3) Due to carbon's small size, it forms extremely strong and stable bonds with other elements