Both magnesium (Mg) and manganese (Mn) react with very dilute cold HNO3 to evolve H2 gas. Magnesium metal reacts with dilute nitric acid to form magnesium nitrate and hydrogen gas Mg+
2HNO3
Cold‌and‌dilute
→
Mg(NO3)2
Magnesiurn‌nitratc
+H2(g) Hydrogen gas is not evolved when other metals react with nitric acid because it is a strong oxidising agents. It oxidises hydrogen produced to water and itself gets reduced to nitrogen oxide.