You are looking at a Medal for Bravery which was first established during the reign of Tsar Alexander II. In the first years of the reign of Emperor Nicholas II, the Medal for Bravery was thoroughly redesigned and its statute changed.
The obverse of the silver Medal for Bravery shows the truncated bust of Tsar Nicholas II facing left encircled by an inscription meaning: "By the Grace of God Nicholas II Emperor and Autocrat of All Russias". The reverse of the Medal bears an inscription meaning: "For Bravery, Fourth Class, No. 642451".