Explanation:

In order to determine the total number of hyperconjugative structures involving C-H bonds possible for but-1-ene, we need to consider the different possible locations of the double bond and the resulting resonance structures.

Structure of but-1-ene:
But-1-ene is an alkene with four carbon atoms and one double bond. The carbon atoms are numbered from 1 to 4, with the double bond between carbons 1 and 2.

Resonance structures:

1. Resonance structure 1:
- In this resonance structure, the double bond is shifted between carbons 2 and 3, resulting in a positive charge on carbon 2 and a negative charge on carbon 3.
- The pi electrons of the double bond are delocalized, resulting in hyperconjugation.
- The C-H bonds on carbons 1, 2, and 3 can participate in hyperconjugation, leading to three hyperconjugative structures involving C-H bonds.

2. Resonance structure 2:
- In this resonance structure, the double bond is shifted between carbons 3 and 4, resulting in a positive charge on carbon 3 and a negative charge on carbon 4.
- The pi electrons of the double bond are delocalized, resulting in hyperconjugation.
- The C-H bonds on carbons 2, 3, and 4 can participate in hyperconjugation, leading to three hyperconjugative structures involving C-H bonds.

3. Resonance structure 3:
- In this resonance structure, the double bond is shifted between carbons 1 and 4, resulting in a positive charge on carbon 1 and a negative charge on carbon 4.
- The pi electrons of the double bond are delocalized, resulting in hyperconjugation.
- The C-H bonds on carbons 1, 2, and 4 can participate in hyperconjugation, leading to three hyperconjugative structures involving C-H bonds.

Total number of hyperconjugative structures:
Adding up the number of hyperconjugative structures from each resonance structure, we get a total of 3 + 3 + 3 = 9 hyperconjugative structures involving C-H bonds.

Correct answer:
The correct answer is (d) 3.