Which substance can not be broken down by a chemical change? a.ammonia b.methanol c.propane d.phosphorus?

The substance that can not be broken down by a chemical change are phosphorus.

Balance Chemical equation is,

                                         P₄  +  10 Cl₂   →   4 PCl₅

According to Balance Equation,

            123.89 g (1 mole) of P₄ reacts to produce   =   4 Moles of PCl₅
Then,
    23 g of P₄ will react with excess Cl₂ to produce   =   X moles of PCl₅

Solving for X,
                                      X  =  (4 mol × 23 g) ÷ 123.89 g

                                      X  =  0.742 g of PCl₅
Result:
           When 23 g of P₄ is reacted with excess Cl₂, 0.742 g of PCl₅ is produced.