Sodium is a soft, light, extremely malleable silver-white metal that reacts explosively with water. chlorine is a highly irritating greenish-yellow gaseous halogen capable of combining with nearly all other elements.
which are most likely the properties of sodium chloride when sodium and chlorine chemically bond in a definite mass ratio to form it?
a. white, solid crystalline powder compound that is fairly stable
b. soft, light, extremely malleable silver-white compound that reacts explosively with water
c. highly irritating greenish-yellow gaseous compound capable of combining with nearly all other elements

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%

well in order to answer this question you have to provide more information < 3