Is the landlord entitled to take the full security deposit because the tenant vacated the leased property before the end of the contract and no replacement tenant was found, even if the tenant refused to pay the consumed electricity bills, claiming that their value is less than the withheld security deposit?

The lease is a binding contract for both parties, and neither may unilaterally terminate it except with the consent of the other. Therefore, if you lease an apartment for a specified period, the full rent for that period becomes binding upon you, and you are not entitled to terminate the contract before its expiration. If you do terminate it, the full rent remains binding upon you. The landlord is entitled to take the security deposit if it is equivalent to the rent for the remaining period. It is not permissible for you to withhold payment of electricity bills in exchange for the security deposit.