Please choose the correct ending to complete the given sentence: Education and Communications: [header] How to synthesise organic compounds [title] Check if the starting chemical is a mixture. [step] If your starting chemical is something like crude oil, you'll need to use distillation or fractional distillation to separate it into parts. [title] See if the starting and target chemicals have any groups in common.

Ending1: [step] Make sure they are all easy to combine. [title] Obtain an active source of this substance. Ending2: [step] For example, they may contain an amine group or a carboxyl group, etc. [title] If the starting chemical is a mixture, look at which parts can be used. Ending3: [step] Each chemical has its group's atomic radius and its " base " number of atoms. To discover the atomic radius, tap a surface with a note board or jot the atomic radius. Ending4: [step] Sometimes they are grouped into what is called a " boundary " area of the 1.5 chemical composition (nacl. ) this area is commonly found in calcium, zinc, and nitrate.

Answer format: ending1/ending2/ending3/ending4