Answer:

Explanation:
The energy difference between the energy levels involved in the transition of the electron is directly proportional to the frequency of the emitted photon:

Where h is the Planck constant. The photon's frequency is inversely proportional to its wavelegth:

Here c is the speed of light. Replacing (2) in (1):

Explanation:
A charge alters the space around it. This alteration of space is called the electric field. It is also defined as the electric force acting on a charged particle per unit test charge. It is given by :

Where
F is the electric force, 
The direction of electric field is in the direction of electric force. For a positive charge, the direction of electric field lines are outwards and for a negative charge, the direction of field lines are inwards.
Hence, the correct option is (c) "electric field".
No, speed is not a vector. it is scalar.
because it doesn't need direction but need magnitude.
Pretty sure that it is 0.