Avalence electron from an arsenic atom might have an electron with the following set of quantum numbers in the ground state.
a. n= 4; l= 1; m1= 0; ms= +â½
b. n= 4; l= 1; m1= 2; ms= ââ½
c. n= 3; l= 1; m1= 0; ms= +â½
d. n= 5; l= 1; m1= â1; ms= ââ½
e. n= 4; l= 2; m1= +1; ms= +â½

A

Explanation:

Arsenic is a p-block non-metal in group 15. It is found in the 4th period with electron configuration [Ar] 3d10 4s2 4p3

The outermost electrons are 4s2 4p3. The quantum number that fits an electron in the 4p orbital is option A

Since n=4,l=1, m= -1,0,1 ms=±1/2

your answer is a. the enthalpy of formation for a pure element in its standard state is always positive.