\(XNO_3\underrightarrow{^{to}}XNO_2+\frac{1}{2}O_2\)
\(n_{XNO_2}=\frac{7,65}{X+14+32}\left(1\right)\)
\(n_{XNO3}=\frac{9,09}{X+14+16.3}\left(2\right)\)
Ta có nXNO2 = nXON3
\(\Leftrightarrow\left(1\right)=\left(2\right)\)
\(\rightarrow X=39\left(K\right)\)
Vậy X là Kali