The cross bridge cycle starts when

a) ca2+ is actively transported into the sarcoplasmic reticulum
b) ca2+ from the sarcoplasmic reticulum binds to troponin
c) atp binds to troponin and is hydrolyzed to adp
d) pi ca2+ from the sarcoplasmic reticulum binds to tropomyosin
e) acetylcholine diffuses away from the synaptic cleft

b) Ca2+ from the sarcoplasmic reticulum binds to troponin

Explanation:

The release of the calcium ions initiates the muscle contractions. The release is triggered from the storage in sarcoplasmic reticulum. These ions initiates contraction that is sustained by the ATP .The ions from sarcoplasm bind to the troponin which drive cross-bridge cycling and pulling of the actin strands by the myosin.

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%