This group of elements in located in the center of the periodic table a. alkaline-earth metals
c. alkali metals
b. halogens
d. transition metals

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(no3)⁻n has oxidation number x,o has oxidation number -2.(x*1 -2*3) charge of the nitrate ion, and we know that charge of the nitrate ion =-1.so,(x*1 -2*3) =-1x-6=-1x=+5answer a. +5.