Which renewability provision allows an insurer to terminate a policy for any reason, and to increase the premiums for any class of insureds?

Answer: Optionally renewable

Explanation:

Optimally renewable provision is the facility in health policy in which an insurer is capable of putting such conditions in the policy so that it can get cancelled or renewal of terms can take place at any time. Cancellation or renewal activity happen when the conditions of policy haven't been met.

This policy provides options for insurer to alter the policy. It also permits the insurer to raise the insurance premium of the insured in case of contract renewal.