I confirm that II is also True apart from I and III.
It depends on the definition of Complete BT the Question setter is following : for II to be true.
Most Author's define it as : Complete BT is a BT in which every node has 2 or 0 children.
Some Author's define it as : Complete BT is a BT where in all nodes have two children and you can remove children from rightmost node as well.
Root has A,B. A has C,D and B has E,F---> complete BT
Now in this example internal nodes=3 and leaves=4
Root has A,B. A has C,D and B has E ----> rightmost child F removed--->still a complete BT.
Now in second example internal nodes=3 and leaves=3.
Hence GATE Questions always specify the convention we are supposed to follow.