Use This Query ,
SELECT
C.student_id,
C.studentname,
M.Guardian_Name
FROM
TableStudent C
OUTER APPLY
(
SELECT TOP 1 *
FROM TableGuardian M
WHERE M.student_id = C.student_id
) m
Since you want to get any guardian I use Top 1 in above Query. If you want to get guardian with Maximum guardian ID for the student, then you can use this
SELECT
C.student_id,
C.studentname,
M.Guardian_Name
FROM
TableStudent C
OUTER APPLY
(
SELECT TOP 1 *
FROM TableGuardian M
WHERE M.student_id = C.student_id
ORDER BY
M.GuardianId DESC
) m
ORDER BY
C.student_id ASC