The number of - CH _ 2 - (methylene) groups in the product formed...

The first reaction is called reductive ozonolysis in which alkene is converted into aldehyde of ketones. In 2nd reaction aldehyde group will be oxidised to carboxylic acid.

The third reaction is called Kolbe's electrolysis reaction in which decarboxylation reaction will occur forming higher alkane.

In last step of reaction aromatisation reaction will take place forming benzene as the major product. This benzene does not contain any ${CH}_{2}$ group.