Which one of the following is constitutionally obligatory on the part of the Prime Minister of India ?

As the President is the supreme commander of the defense forces, the Prime Minister has to take all major decisions regarding defense only after prior approval by the President.

The Prime Minister has to communicate to the President all decisions of the Cabinet relating to administration and proposals for legislation 

As the ministers are appointed by the President, the Prime Minister has to go by President             discretion in the allocation of business among the ministers.

The Prime Minister, if the happens to be the leader of a party not having the required majority should prove his majority strength in both the Houses of Parliament within the period stipulated by the President