Identify the reaction type

This is a dehydrohalogenation / elimination reaction of a haloalkane. In such reactions, the major product is usually the more stable alkene, and if multiple eliminations occur, the more conjugated and more substituted diene is favored.

Analyze the carbon skeleton implied by the options

All options correspond to a phenyl-substituted heptadiene. The important issue is:

• where the phenyl group is located, and
• where the double bonds are located.

Apply stability principles

The most stable product will be the one having maximum stabilization due to:

• conjugation between the two double bonds,
• greater alkene substitution, and
• conjugation of the double bond with the phenyl ring whenever possible.

Compare the options

• A: 6-Phenylhepta-3,5-diene
  Double bonds at $3,5$ are conjugated, but the phenyl group at C-6 gives a structure equivalent to a terminal side chain near phenyl; this is less favored compared with a structure where the alkene system is better substituted near the phenyl-bearing carbon.

• B: 6-Phenylhepta-2,4-diene
  This is also a conjugated diene, but the phenyl group is farther from the more substituted arrangement obtainable when phenyl is at C-2.

• C: 2-Phenylhepta-2,4-diene
  Here the product is a conjugated diene ($2,4$-diene), and the double bond at C-2 is directly associated with the phenyl-substituted carbon, giving extra stabilization. This makes it the most stable among the given options.

• D: 2-Phenylhepta-2,5-diene
  The double bonds at $2,5$ are isolated, not conjugated, so this is less stable than option C.

Conclusion

The major product is the most stable conjugated diene, namely: $\boxed{\text{2-Phenylhepta-2,4-diene}}$

Compare with stored correct answer

Stored correct answer = C
Derived answer = C
Hence, they agree.