Consider the following reversible reaction.
.
What is the equilibrium constant expression for the given system?
a.
b.
c.
d.

No one is correct. The correct expression is:

Keq = [H₂]²  . [O₂]² / [H₂O]²

Explanation:

To build the Keq expression in a chemical equilibrium you must consider the molar concentrations of reactants / products, and they must be elevated to the stoichiometric coefficient.

The balance reaction is:

2 H₂O (g)  ⇄  2 H₂ (g)  +  O₂ (g)

Keq = [H₂]²  . [O₂]  / [H₂O]²

In opposite side: 2 H₂ (g)  +  O₂ (g)   ⇄  2 H₂O (g)

Keq =  [H₂O]² / [H₂]²  . [O₂]  

i don't see a text, but i am gonna assume this *orbit* the curved path, usually elliptical, described by a planet, satellite, spaceship, etc., around a celestial body, as the sun.

"record the time to complete a chemical reaction" would most likely be part of a lab procedure.