Answer:
3
Explanation:
2x5 is 10 then 13-10 is 3
 
        
                    
             
        
        
        
Answer:
ΔHrxn = [(1) -1675.5 ( kJ/mole) + (2) 0 ( kJ/mole)] - [(1) -824.3 ( kJ/mole) + (2) 0 ( kJ/mole)]
Explanation:
ΔHrxn = 2ΔHf (Al₂O₃)  - ΔHf (Fe₂O₃) 
Remember that for pure elements in their standard state of temperature and pressure by definition their standard heats of formation are zero.
ΔHrxn = 2(-1675.7) - (-824.3) kJ/mol
ΔHrxn = 2527 kJ/mol
 
        
             
        
        
        
Atomic number = No. of proton = 1
so, your answer is 1