1) When concentration of reactant increases more collision will ocuur between them and more product is formed.
so incresing the concentration of I2 will shift reaction towards the product
2) It is just the opposite case of (1) where it will shift backward
3) Upon elevation of the temperature, equilibrium shifts in the direction of the endothermic reaction (i.e. aside reaction, running with absorbing a heat.
Here the enthalpy of formation is positive indicates that the process is endothermic in nature , because the enthalpy of the products is higher than the enthalpy of the reactants of the system. So the rate will shift towards the product.
4) When the pressure is increased by compressing a system, equilibrium shifts in the direction of a reduction in the number of molecules of the gases (i.e. in the direction of lowering pressure). Here less no of moles are present at reactant side so the process will shift towards the reactant.