We investigate the structure and activated dynamics of a binary mixture of colloidal particles dispersed in a

solvent of much smaller-sized particles. The solvent degrees of freedom are traced out from the grand partition

function of the colloid-solvent mixture which reduces the system from ternary to effective binary mixture of

colloidal particles. In the effective binary mixture colloidal particles interact via effective potential that consists

of bare potential plus the solvent-induced interaction. Expressions for the effective potentials and pair correlation

functions are derived. We used the result of pair correlation functions to determine the number of particles in

a cooperatively reorganizing cluster (CRC) in which localized particles form “long-lived” nonchemical bonds

with the central particle. For an event of relaxation to take place these bonds have to reorganize irreversibly, the

energy involved in the processes is the effective activation energy of relaxation. Results are reported for hard

sphere colloidal particles dispersed in a solvent of hard sphere particles. Our results show that the concentration

of solvent can be used as a control parameter to fine-tune the microscopic structural ordering and the size of

CRC that governs the glassy dynamics. We show that a small variation in the concentration of solvent creates

a bigger change in the kinetic fragility which highlights a wide variation in behavior, ranging from fragile to

strong glasses. We conclude that the CRC which is determined from the static pair correlation function and the

fluctuations embedded in the system is probably the sole player in the physics of glass transition.