Question

how to know which metal is more reactive

Answer 1

by seeing the reactivity series...
potassium(K)
sodium(Na)
calcium(Ca)
magnesium(Mg)
Aluminum (Al)
zinc(Zn)
iron(Fe)
lead(pb)
hydrogen(H)
copper(cu)
mercury( hg)
gold (ag)
silver(au)

it is in decreasing order...
the above metals are more reactive than the lower metals...

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Answer 2

The primary difference between metals is the ease with which they undergo chemical reaction. the element towards the bottom left corner of the periodic table are the metals which are most reactive.
Example. sodim and pottassium

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