Yes, it is possible to combine the same two elements to form two different compounds. An example is carbon dioxide CO2 and carbon monoxide CO. This is because two elements can form different types of bond and end up with different compounds.
There is a limited number of elements but a large number of compounds because of the above reason.
A car sitting still
The distance is not changing which means the car is not moving
In case of heptane (C7H16) the following structural isomers are possible
shown in figure
a. 1-sec-butylpropane : this is actually 3-methyl hexane
b. 4-methylhexane : this is actually 3-methylhexane
c. 2-ethylpentane : this is actually 3-methyl hexane
d. 1-ethyl-1-methylbutane: 3-methylhexane
e. 3-methylhexane: correct IUPAC
f. 4-ethylpentane: This is actually 3-methylhexane
Hence all represent single isomer