Answer:
the answer is d. but try 20
Explanation:
1 endothermic 2 yes and exothermic 3 endothermic
Explanation:
In nitrate ion that is 
,have negative charge on overall ion. Negative charge on the one oxygen atom is de-localized to other oxygen atoms present in the molecule of a nitrate ion. Due to this resonance nitrate ions get stabilized.
For resonance structures for the nitrate ion, refer to image attached.
First, we need to get the number of moles:
from the reaction equation when Y4+ takes 4 electrons and became Y, X loses 4 electrons and became X4+
∴ the number of moles n = 4
we are going to use this formula:
㏑K = n *F *E/RT
when K is the equilibrium constant = 4.98 x 10^-5
and F is Faraday's constant = 96500
and the constant R = 8.314
and T is the temperature in Kelvin = 298 K
and n is number of moles of electrons = 4
so, by substitution:
㏑4.98 x 10^-5 = 4*96500*E / 8.314*298
∴E = -0.064 V
