The substance in the block is copper.
To identify the substance, we can use the following steps:
1. Calculate the specific heat capacity of the substance using the equation:`

where:
* C is the specific heat capacity

* q is the amount of heat absorbed (J)
* m is the mass of the substance (g)
* ΔT is the change in temperature (°C)
Substituting the known values, we get:
C = 2340 J / 300 g * (45°C - 25°C)
= 0.39

2. Look up the specific heat capacity of different substances in the table provided.
3. The substance with the specific heat capacity closest to 0.39
is copper.
Therefore, the substance in the block is copper.
Answer: Copper