What is the electron configuration of Ag?

Electronic configuration can be defined as the arrangement of electrons in the orbital and shell of an element. 

It is used to determine the position of the element in the periodic table that determine the group and row for a particular element in the periodic table, it also determines the stability, valency of an element, and other chemical properties of that particular element. 

Silver(Ag) has atomic number 47 and belongs to group 11 as it has only one electron in its outermost shell.

It is a d-block element as the last electron of silver is present in the d subshell. The maximum electron that can be accommodated in d subshell is 10. 

The General configuration of d subshell is:$(\mathrm{n}-1){\mathrm{d}}^{(1-10)}{\mathrm{ns}}^{(0-2)}$. 

The electronic configuration in general as per rule becomes: $1{\mathrm{s}}^{2}2{\mathrm{s}}^{2}2{\mathrm{p}}^{6}3{\mathrm{s}}^{2}3{\mathrm{p}}^{6}3{\mathrm{d}}^{10}4{\mathrm{s}}^{2}4{\mathrm{p}}^{6}4{\mathrm{d}}^{9}5{\mathrm{s}}^2$
But, in this case, there is an exception as every element tries to attain noble gas configuration silver also tries to attain the nearest noble gas which is Krypton configuration to attain stability by shifting one electron to d subshell from s subshell thus completely filling it. 

Thus, the electronic configuration will be$1{\mathrm{s}}^{2}2{\mathrm{s}}^{2}2{\mathrm{p}}^{6}3{\mathrm{s}}^{2}3{\mathrm{p}}^{6}3{\mathrm{d}}^{10}4{\mathrm{s}}^{2}4{\mathrm{p}}^{6}4{\mathrm{d}}^{10}5{\mathrm{s}}^1$
 Hence, option C is correct.