The correct answer is option 'B' - Pahadpur Copper Plate.

Explanation:
The Pahadpur Copper Plate inscription is considered to contain the most decisive evidence in favor of the exclusive ownership of land by the state or the king during the Gupta period. Here is a detailed explanation of why this inscription holds such significance:

1. Historical Background:
The Gupta Empire, which existed from the 4th to the 6th century CE, was known for its administrative and legal systems. The ownership and control of land were crucial aspects of governance during this period.

2. Contents of the Pahadpur Copper Plate Inscription:
The Pahadpur Copper Plate inscription is an important epigraphic record from the Gupta period. It was discovered in Pahadpur village in the present-day state of Madhya Pradesh, India. The inscription is written in Sanskrit and belongs to the reign of King Kumaragupta I.

3. Decisive Evidence:
The Pahadpur Copper Plate inscription provides decisive evidence in favor of the exclusive ownership of land by the state or the king. It mentions the grant of land to a Brahmana named Devapala by King Kumaragupta I. The inscription clearly states that the land was granted to Devapala "from time immemorial."

4. Exclusive Ownership by the State:
The use of the phrase "from time immemorial" in the Pahadpur Copper Plate inscription implies that the land belonged exclusively to the state or the king even before the grant was made. This suggests that the state or the king had complete ownership and control over the land, and they had the authority to grant or allocate it to individuals.

5. Importance of Exclusive Ownership:
The concept of exclusive ownership of land by the state or the king was significant during the Gupta period as it provided the basis for the administration and taxation of land. It allowed the state to collect revenue and maintain control over agricultural production.

In conclusion, the Pahadpur Copper Plate inscription is considered to contain the most decisive evidence in favor of the exclusive ownership of land by the state or the king during the Gupta period. This inscription supports the idea that the state or the king had complete authority over the land and the power to grant or allocate it to individuals.