Question

Isomers always have:
A. same chemical properties
B. same molecular formula
C. same chemical structure
D. none of the above

Answer 1

The chemical compounds can exist in various structural forms. These structural forms have different arrangements of atoms. ‘iso’ means the same while ‘mer’ means units. Isomerism is the property that compounds can possess by having various isomers. There can be various types of isomers that can have different structures, functional groups, etc.

Complete answer:
Chemical compounds can possess various structural representations, but having the same molecular formula. These are called isomers and the property is called isomerism. The isomer name itself means that ‘iso’ is the same and ‘mer’ units. This means the same units or atoms. The difference in these is just that they can possess different structures.
For example, a compound with molecular formula ${{C}_{3}}{{H}_{8}}O$ can have different forms of structures of alcohol like; 1-propanol whose structure has OH functional group at 1st carbon as $C{{H}_{3}}C{{H}_{2}}C{{H}_{2}}OH$ and 2-propanol whose structure has OH group at the second carbon atom as $C{{H}_{3}}CH(OH)C{{H}_{3}}$
A 3rd isomer is also possible when we do not consider alcohol as functional group, and consider an ether as a functional group that has formula R – O – R, where R is the alkyl group, so with 3 carbon it can be:
Ethyl methyl ether whose structure has O in the center and an ethyl and methyl group at the ends as,$C{{H}_{3}}-C{{H}_{2}}-O-C{{H}_{3}}$ .
Hence, isomers always have the same molecular formula.

So, option B is correct.

Note:
The isomers can also be differentiated according to the positions like, chain, position, structure, geometric, functional isomers are various types. These include different positions of the alkyl groups in chain , position and structure isomerism, while different positions of functional groups in functional isomers.