Question

Which is the general formula of alkanes?
(A) ${{C}_{n}}{{H}_{2n+2}}$
(B) ${{C}_{n}}{{H}_{2n}}$
(C) ${{C}_{n}}{{H}_{2n-2}}$
(D) None of the above

Answer 1

Hint: Check the formula which is appropriate for alkanes by using one of the alkanes like methane having a molecular formula of $C{{H}_{4}}$with one carbon atom, where n = 1 (n= no of carbon atom)

Complete step by step solution:
Firstly we should know some important points about the alkanes that are:
- They are unsaturated hydrocarbons
- They contain only single bonds and not the double or triple bond (unsaturated)
- There will be sharing of only one pair of electrons between each other.
  For example we take methane having a molecular formula of $C{{H}_{4}}$.
In methane one carbon is attached with four hydrogen atoms, and they are singly bonded.
- Carbon having four valence electrons share one of its electrons with each hydrogen atom to complete its octet and in this way hydrogen completes its duplet to form a stable compound.
- Now to find the general formula for an alkane you can check all the options given in the question to find the correct one with the example of methane itself,
- Let us take the first case which is ${{C}_{n}}{{H}_{2n+2}}$ , where n= no of carbon atom,
 We have seen that methane have only one carbon atom, n= 1
  By putting the value of n in first case we get,
\[{{C}_{1}}{{H}_{2\times 1+2}}=\,C{{H}_{4}}\]
 This case is satisfying the condition for alkane.
- Let us take one more case which is ${{C}_{n}}{{H}_{2n}}$
  By putting the value of n in this case we get,
\[{{C}_{1}}{{H}_{2\times 1}}=\,C{{H}_{2}}\]
- In this case you can see that they are not satisfying the condition.

Thus the correct option will be (A)

Note: Check carefully the no of carbon atoms when putting the value of n in the formula. Do not confuse between the n of hydrogen and carbon, n only represent the no of carbon atoms in both the cases.