\(n_K=\dfrac{m}{M}=\dfrac{7,8}{39}=0,2\left(mol\right)\)
\(a,PTHH:4K+O_2\rightarrow2K_2O\)
\(0,2:0,05:0,1\left(mol\right)\)
\(K_2O+H_2O\rightarrow2KOH\)
\(0,1:0,1:0,2\left(mol\right)\)
\(b,V_{O_2}=n.22,4=0,05.22,4=1,12\left(l\right)\)
\(c,m_{KOH}=n.M=0,2.\left(39+16+1\right)=0,2.56=11,2\left(g\right)\)