A scientist is experimenting with a reaction of hydrocarbon compound B in the presence of UV light. In his observation, he found that compound B releases reddish-brown gas when undergoing halogenation process to produce compound D. Different experiment was carried out for compound B and the result showed that the products obtained were geometrical isomer compound. 

1.Identify the name of hydrocarbon compound B and draw their possible condensed and skeletal structures. 

2.Predict the mechanism reaction that occurs for the formation of compound D. 

3.Identify what type of functional group present in geometrical isomer compounds. 

4.Illustrate the geometrical isomer compounds and justify why they have different physical properties.