Final answer:
The exact length of the metal at 125 °C cannot be determined without the coefficient of linear expansion. The metal will expand somewhat from its original length of 2.3 cm, but without the coefficient, the exact new length cannot be calculated.
Step-by-step explanation:
When a metal is heated, it expands due to an increase in kinetic energy causing the atoms to move further apart. The increase in length of the metal can be calculated if the coefficient of linear expansion is known. Unfortunately, without the coefficient of linear expansion for the specific metal given in the question, we cannot exactly calculate the new length of the metal at 125 °C. Generally, the difference in temperature and the original length are used alongside this coefficient in a formula to find the change in length, which is then added to the original length to get the total length at the new temperature.
However, since the metal in question has a melting point of 400 °C and it is only heated to 125 °C, we can infer that the change in length is not enough to melt the metal and it will likely remain a solid with a somewhat longer length, assuming a normal coefficient of linear expansion for metals.