Asample of a gas is contained in a closed rigid cylinder. according to kinetic molecular theory, what occurs when the gas inside the cylinder is
heated?
(1) the number of gas molecules increases.
(2) the number of collisions between gas molecules per unit time decreases.
(3) the average velocity of the gas molecules increases.
(4) the volume of the gas decreases.

The answer is (3) The average velocity of the gas molecules increases. In the closed rigid cylinder, the volume of the gas and number of gas molecules will not change. The number of collision will increase.

When a sample of a gas is contained in a closed rigid cylinder and the gas inside the cylinder is heated "(3) The average velocity of the gas molecules increases". The number of molecules stays the same. 

Answer is: the equilibrium  shifts toward the reactants, to the left side of chemical reaction.it is because lead(ii) nitrate dissociates in water: pb(no₃)₂ → pb²⁺(aq) + 2no₃⁻(aq).according to lechatelier's principle, the position of equilibrium moves to counteract thechange (more lead cations, common ion), the position of equilibrium will move so that the concentration ofproducts decrease and concentration of reactants of chemical reaction increase.read more on -