  A computation shows that there are 77 (up to scalar shifts) possible pairs of
integer coefficient polynomials of degree five, having roots of unity as their
roots, and satisfying the conditions of Beukers and Heckman [1], so that the
Zariski closures of the associated monodromy groups are either finite or the
orthogonal groups of non-degenerate and non-positive quadratic forms. Following
the criterion of Beukers and Heckman [1], it is easy to check that only 4 of
these pairs correspond to finite monodromy groups and only 17 pairs correspond
to monodromy groups, for which, the Zariski closures have real rank one.
  There are remaining 56 pairs, for which, the Zariski closures of the
associated monodromy groups have real rank two. It follows from Venkataramana
[16] that 11 of these 56 pairs correspond to arithmetic monodromy groups and
the arithmeticity of 2 other cases follows from Singh [11]. In this article, we
show that 23 of the remaining 43 rank two cases correspond to arithmetic
groups.
