\[\boxed{\mathbf{2}.}\]
\[\textbf{а)}\ \frac{a^{21} \cdot a^{13}}{a^{31}} = \frac{a^{34}}{a^{31}} = a^{3}\]
\[при\ a = 1,6:\]
\[(1,6)^{3} = 4,096.\]
\[при\ a = - 0,11:\]
\[( - 0,11)^{3} = - 0,001331.\]
\[\textbf{б)}\ \frac{n^{48}}{n^{19} \cdot n^{26}} = \frac{n^{48}}{n^{45}} = n^{3}\]
\[при\ n = 0,3:\]
\[(0,3)^{3} = 0,027.\]
\[при\ n = - 0,4:\]
\[( - 0,4)^{3} = - 0,064.\]