Write the structural formula of the third compound of homologous series of alkane.

To find the third alkane in the homologous series, we will use the general formula of alkanes, CnH2n+2, where n is the number of carbon atoms in the alkane. For the third alkane, n will be 3. The formula of the third alkane can be written as C3H8.

With the formula, C3H8, we can now draw the structural formula of the third alkane, also known as propane. We have 3 carbon atoms and 8 hydrogen atoms. The three carbon atoms are in a straight chain with a single bond between each pair of adjacent carbon atoms. Each carbon atom should have four bonds. For Carbon-1 (the first carbon), there is a bond with Carbon-2, so it will have three more bonds with hydrogen atoms. Similarly, Carbon-3 (the third carbon) has one bond with Carbon-2, so it will also have three more bonds with hydrogen atoms. Carbon-2 (the second carbon) has two bonds with Carbon-1 and Carbon-3, so it will have two more bonds with hydrogen atoms. Therefore, the structural formula for propane, the third alkane, is as follows: H H H | | | C-C-C | | | H H H