Which of the following is a gas-evolution reaction?
a. 2 c2h6(l) + 7 o2(g) → 4 co2(g) + 6 h2o(g)
b. nh4cl(aq) + koh(aq) → kcl(aq) + nh3(g) + h2o(l) 2
c. h2(g) + o2(g) → 2 h2o(g)
d. licl(aq) + nano3(aq) → lino3(aq) + nacl(aq)
e. none of the above are gas-evolution reactions.

B. NH₄Cl(aq) + KOH(aq) → KCl(aq) + NH₃(g) + H₂O(l)

Explanation:

A gas-evolution reaction is defined as a chemical reaction that produce a gas and where reactants are not in gaseous phase.

Thus, the reactions:

A. 2C₂H₆(l) + 7O₂(g) → 4CO₂(g) + 6H₂O(g)  Is not a gas-evolution reaction because one reactant is a gas.

B. NH₄Cl(aq) + KOH(aq) → KCl(aq) + NH₃(g) + H₂O(l) Is a gas-evolution reaction because one product is the NH₃ that is a gas and reactants are not gases.

C. 2H₂(g) + O₂(g) → 2H₂O(g)  Is not a gas-evolution reaction because the reactants are gases

D. LiCl(aq) + NaNO₃(aq) → LiNO₃(aq) + NaCl(aq) Is not a gas-evolution reaction because there are not gases as products.

I hope it helps!

here we have to get the change of moles on decrease the volume of the reaction in gas phase.

the   per the given options it will decrease by (d) 11-50%

we know, on decreasing the volume of the gas phase reaction the reaction moves to the product side.

the reaction:                     so₂cl₂ (g) = so₂ (g) + cl₂ (g)         total

the moles at equilibrium:   1 - α                 α               α           = 1+α

concentrations:                   1 - α               α               α           = 1 + α

(concentration = moles/volume, as volume is 1 l)

(where α is the degree of dissociation)

now the dissociation constant in terms of concentration is :

=  

or,

or,   = (at v = 1l)

the reaction:                     so₂cl₂ (g) = so₂ (g) + cl₂ (g)         total

the moles at equilibrium:   1 - α                 α               α           = 1+α

concentrations:               (1 - α)/0.5           α/0.5         α/0.5       = (1 + α)/0.5

thus, the dissociation constant in terms of concentration is :

or,  

=  

so, the change of 1 : 1/0.5

or, 1: 2

thus it will decrease by 50%.

or, as per the given options it will decrease by 11-50%