What happens to capacitor when capacitor is fully charged upon connecting to dc voltage source, will it behave as open circuit ?
One the capacitor is fully charged, theoretically it will act like an open circuit. As no DC is able to pass, there will be no current flow and the voltage on the capacitor will be equal to the supply. Of course, in real life there will be a small amount of leakage and the voltage will never be exactly equal!
Anyhow, to answer the question, yes. In a DC application, once a capacitor is fully charged, it acts like an open circuit.
As mentioned above, a capacitor will be an open circuit once fully charged. The voltage across the capacitor will be equal to the voltage source.
I believe there was another question above about why use a capacitor when there is DC. If you haven't had training in AC electronics, I'll give you the short: when AC and DC currents are both flowing in the same wire, the DC current cannot pass through the capacitor, but the AC can!
This is a simple way to block DC current from entering parts of our circuit that only focus on AC. Capacitors are also used for filtering, coupling, decoupling, etc.