Answer
a) Physical
b) Physical
c) Chemical
d) Chemical
Work Step by Step
a) Change in the state of matter (solid to gaseous) is a physical change.
b) Molecules occupy more space as their average energy increases: physical change.
c) Combustion reaction converts methane and oxygen into carbon dioxide and water vapor, releasing heat: chemical reaction implies chemical change.
d) NaCl is an ionic compound, when dissolved in water It breaks into íons ($Na^+$ and $Cl^-$), which is a chemical change.
