\[\boxed{\mathbf{2.}}\]
\[11 - 4 = 11 - 1 - 3 = 10 - 3 =\]
\[= 7\]
\[12 - 5 = 12 - 2 - 3 = 10 - 3 =\]
\[= 7\]
\[13 - 7 = 13 - 3 - 4 = 10 - 4 =\]
\[= 6\]
\[14 - 5 = 14 - 4 - 1 = 10 - 1 =\]
\[= 9\]
\[16 - 8 = 16 - 6 - 2 = 10 - 2 =\]
\[= 8\]
\[15 - 9 = 15 - 5 - 4 = 10 - 4 =\]
\[= 6\]
\[12 - 9 = 12 - 2 - 7 = 10 - 7 =\]
\[= 3\]
\[13 - 7 = 13 - 3 - 4 = 10 - 4 =\]
\[= 6\]
\[16 - 8 = 16 - 6 - 2 = 10 - 2 =\]
\[= 8\]