What is the maximum total number of groups that one user can concurrently belong to?

A user account must be a member of a primary group, and may also be a member of one or more
secondary groups. What is the maximum total number of groups that one user can concurrently
belong to?

A.
15

B.
16

C.
17

D.
63

E.
64

F.
65

G.
The number of groups one user can concurrently belong to is unlimited in Solaris 11.

Explanation:
Each user belongs to a group that is referred to as the users primary group. The
GID number, located in the users account entry within the /etc/passwd file, specifies the users
primary group.
Each user can also belong to up to 15 additional groups, known as secondary groups. In the
/etc/group file, you can add users to group entries, thus establishing the users secondary group
affiliations.
Note (4 PSARC/2009/542):
his project proposes changing the maximum value for NGROUPS_MAX
from 32 to 1024 by changing the definition of NGROUPS_UMAX from 32
to 1024.
The use for a larger number of groups is described in CR 4088757,
particular in the case of Samba servers and ADS clients; the
Samba servers map every SID to a Unix group. Users with more
than 32 groups SIDs are common. We’ve seen reports varying from
“64 is enough”, “128 is absolutely enough” and “we’ve users with
more 190 group SIDS).
NGROUPS_MAX as defined by different Unix versions are as follows
(http://www.j3e.de/ngroups.html):

Linux Kernel >= 2.6.365536
Linux Kernel < 2.6.332
Tru64 / OSF/132
IBM AIX 5.264
IBM AIX 5.3 … 6.1128
OpenBSD, NetBSD, FreeBSD, Darwin (Mac OS X)16
Sun Solaris 7,8,9,1016 (can vary from 0-32)
HP-UX20
IRIX16 (can vary from 0-32)
Plan 9 from Bell Labs32
Minix 30 (Minix-vmd: 16)
QNX 6.48
Reference: Increase the maximum value of NGROUPS_MAX to 1024 PSARC/2009/542