The valence electrons of a krypton (Kr) atom in the ground state are located in the A. first energy level (shell).

B. second energy level (shell).

C. third energy level (shell).

D. fourth energy level (shell).

D

Explanation:

The valence electrons are the outer electrons and must be located in the outermost shell. In this case, D.

the enthalpy of formation of water is given as -285.8kj/mol, which states that the enthalpy of formation is negative.

negative enthalpy of formation indicates that the heat is released during the reaction process. the heat is released from reaction to the surroundings the enthalpy is expressed with a negative sign with the energy given out in the reaction process.

the formation of water takes place by giving out heat which is -285.8 kj/mol.