Answer: 3 significant figures
Explanation: because in scientific notation only the before and after decimal number are considered but in standard form all numbers including exponents are all significant figures
 
        
                    
             
        
        
        
Answer:

Explanation:
Hello,
In this case, for latent heat (phase change) we need to consider the enthalpy associated with the involved process, here, melting or fusion; thus, the enthalpy of fusion of copper is 13.2 kJ/mol, therefore, the heat is computed as:

Nevertheless, since the given enthalpy is per mole of copper, we need to use its atomic mass to perform the correct calculation as follows:

Which is positive as it needs to be supplied to the system.
Best regards.
 
        
             
        
        
        
3. Decreases
The concentration of hydrogen ions increasing creates an acid, which is 7 or below on the pH scale. If the pH value lessens from 7 to create an acid, that would mean it decreases.