Answered

A reaction is most likely to occur when reactant particles collide with
(1) proper energy, only
(2) proper orientation, only
(3) both proper energy and proper orientation
(4) neither proper energy nor proper orientation



Answer :

A reaction is most likely to occur when reactant particles collide with proper energy ONLY. Or with sufficient energy.
PBCHEM
Correct Answer: (3) both proper energy and proper orientation

Reason:
The reactants requires certain threshold energy so that they can react to form compound. This energy is called as activation energy. In addition to this, orientation of reactants molecules are important. If the steric orientation of molecule is not proper, then the collision will not result in formation of product. This is based on collision theory of chemical kinetics.