Reaction b,c and d could be written as net ionic equations.
Further explanation
The electrolyte in the solution produces ions.
The equation of a chemical reaction can be expressed in the equation of the ions
For strong electrolytes (the ionization rate = 1) is written in the form of separate ions, while the weak electrolyte (degree of ionization <1) is still written as an un-ionized molecule
In the ion equation, there is a spectator ions that is the ion which does not react because it is present before and after the reaction
When these ions are removed, the ionic equation is called the net ionic equation
For gases and solids including water (H₂O(l)) can be written as an ionized molecule
So only the dissolved compound is ionized ((expressed in symbol aq)
To see the reaction can be expressed in terms of the net ionic equation, we must see that there are two or more ions that are the same from both sides of the reactant and the product in the form of aquoeus (because the form of compounds in the form of gases, solids and liquids will remain molecular and non-ionized)
CH4 (g) + 2 O2 (g) = CO2 (g) + 2 H2 O(g)
No⇒no compounds in the aqueous form
Cu(s) + 2 AgNO3 (aq) = 2 Ag(s) + Cu(NO3 )2 (aq)
Cu(s) + 2 Ag⁺+ 2NO3⁻ (aq) = 2 Ag(s) + Cu²⁺ +2NO3⁻ (aq)
Cu(s) + 2 Ag⁺(aq) = 2 Ag(s) + Cu²⁺(aq)
yes, because there are NO3 (spectators ion) on both sides
MgCl2 (aq) + 2 KOH(aq) = Mg(OH)2 (s) + 2 KCl(aq)
Mg²⁺(aq)+2Cl⁻ (aq) + 2K⁺(aq)+2OH⁻(aq) = Mg(OH)2 (s)+ 2K⁺(aq)+2Cl⁻(aq)
Mg²⁺(aq)+2OH⁻(aq) = Mg(OH)2 (s)
yes, because there are 2Cl⁻ (aq) and 2K⁺(aq (spectators ion) on both sides
CaCO3 (s) + 2 HCl(aq) = CaCl2 (aq) + CO2 (g) + H2 O(l)
CaCO3 (s) + 2 H⁺(aq)+2Cl⁻(aq) = Ca²⁺(aq)+2Cl⁻ (aq) + CO2 (g) + H2 O(l)
CaCO3 (s) + 2 H⁺(aq) = Ca²⁺(aq) + CO2 (g) + H2 O(l)
yes, because there are Cl⁻ (spectators ion) on both sides