Answer:
A) calcium-0 B) gallium-1 C) silicon-2 D) vanadium-3 E) carbon-2 F) neon-0
Step-by-step explanation:
Hund's rule of maximum multiplicity:- 
Firstly, every orbital which is present in the sublevel is singly occupied and then the orbital is doubly occupied. 
(A) Calcium. 
The electronic configuration is - 
 
Thus, 4s orbital is fully filled and thus there is no singly filled orbital in calcium.
(B) Gallium. 
The electronic configuration is - 
 
Thus, 4s orbital is fully filled and p orbital can singly filled 3 electrons. Thus, no electrons will be paired and thus, 1 orbital will be singly filled in gallium. 
(C) Silicon. 
The electronic configuration is - 
 
Thus, 3s orbital is fully filled and p orbital can singly filled 3 electrons. Thus, no electrons will be paired and thus, 2 orbitals will be singly filled in silicon. 
D) Vanadium
The electronic configuration is - 
 
Thus, 4s orbital is fully filled and d orbital can singly filled 5 electrons. Thus, 3 orbitals will be singly filled in vanadium. 
(E) Carbon. 
The electronic configuration is - 
 
Thus, 2s orbital is fully filled and p orbital can singly filled 3 electrons. Thus, Carbon has 2 singly occupied orbitals. 
F) Neon
The electronic configuration is - 
 
Thus, 2s orbital is fully filled and p orbital can singly filled 3 electrons which is also fully filled. So, there is no singly filled orbital in neon.