Identity each of the following catalysts as
homogeneous or heterogeneous.
the addition of a strip of solid platinum metal to an
aqueous solution of hydrogen peroxide increases
the reaction rate of the decomposition reaction

Platinum is a Heterogeneous catalyst  

Explanation:

Catalyst are substance that speed up the rate of a chemical reaction . Catalyst increases the rate of a chemical reaction by lowering it activation energy. During the reaction, the catalyst are not consumed. In other words, catalyst does not change in amount as it does not go into the reaction.

Catalyst can be homogeneous or heterogeneous . A homogeneous catalyst is one which phase(liquid or gas) is same as the reactant phase. Heterogeneous catalyst are catalyst which phase(solid) is different from the reactants phase.      

From the reaction above

2H2O(aq)    Pt(s)→    2H2O(l) + O2(g)

Platinum is at the solid phase which is a different phase from the reactant(Hydrogen peroxide) which is Aqueous.

Since platinum is of a different phase , it is a heterogeneous catalyst.