Tollens’ reagent can be obtained by mixing aqueous ${\mathrm{AgNO}}_3$with aqueous NH₃solution. The reagent mainly contains. 

Ammonical silver nitrate solution, a colourless, basic, aqueous solution with silver ions coordinated to ammonia, constitutes Tollen's reagent.
Aldehydes and ketones can be identified using the Tollens Test. The silver mirror test is another name for this arbitrary laboratory procedure.
Therefore, the correct option is option (A)${\left[\mathrm{Ag}{\left({\mathrm{NH}}_3\right)}_2\right]}^{+}$.