Which of the following elements is a metal?a.₁₁x²³b.₉Y¹⁹c.₁₀Z²⁰

a.₁₁x^{23 
Atomic number, Z = 11 (number of protons)
Mass number, A = 23 (number of nucleons, protons an neutrons).
Element is Na which is a metal.}
b.₉Y19
Z=9,    A =19
element is F, which is a non-metal
c.₁₀Z20

Z=10,  A= 20
Element is Ne, non-metal (noble gas)

So, answer is option a