Disproportionation reactions are the reactions in which a compound undergoes oxidation as well as reduction. CaCO3→CaO+CO2 is an example of decomposition reaction. There is no simultaneous oxidation or reduction happening. ∴ It is not an example of disproportionation reaction. Rest all examples
0
P
4+3‌NaOH+3H2O→3NaH2
+1
PO2
+
−3
PH3
‌2H2
−1
O2
→2H2
−2
O
+
0
O2
‌
+1
2Cu+
→
2+
Cu
+
0
Cu
The element undergoes oxidation and reduction both. Hence, are examples of disproportionation reactions.