Hydrogen is not obtained when zinc reacts with:
(a) cold water
(b) dil. H2SO4
(c) dil HCl
(d) hot 20% NaOH
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(a) Elements having reduction potential of -0.41V or below can liberate hydrogen from cold water. Such as alkali metals Ba, Sr and Ca.
Also Zn-Cu and Al-Hg couples liberate hydrogen with cold water.