Here scribe 2 of 𝓟 wrote the singular hand, but otherwise the Book of Mormon text avoids the singular hand for expressions of this type. Elsewhere the text has only the plural hands in instances of “delivering someone into the hands of X” (17 times), “delivering someone out of the hands of X” (32 times), and “delivering someone from the hands of X” (2 times). There are no other examples of this type that take the singular hand.
In addition, there is abundant evidence in the manuscripts that the scribes frequently wrote hand instead of the correct hands. In the following list, we have ten examples where the scribe initially wrote hand but then corrected it to hands; Oliver Cowdery is responsible for seven of the examples, scribe 2 of 𝓟 for the remaining three (each of the latter is marked below with an asterisk):
Thus the chances are quite high that the singular hand in 𝓟 for Alma 5:4 is an error for hands.
Of course, the singular hand is possible in English. In fact, when we consider similar usage in the King James Bible, we find evidence for both singular hand and plural hands, as in the following sampling from the first part of the King James Old Testament:
In all these examples, the original Hebrew uses the singular for two distinct Hebrew words meaning ‘hand’; thus the variation in number in the King James Bible derives from usage in Early Modern English. Since for this type of expression the singular hand is possible in the King James Bible, the critical text will accept the singular hand in Alma 5:4, the reading of the earliest extant textual source (the printer’s manuscript), even though the odds are high that this instance of the singular hand is a scribal error for hands.
Summary: Restore in Alma 5:4 the singular hand in “they were delivered out of the hand of the people of king Noah”; the reading in the singular is based on the earliest extant textual source for this passage (namely, the printer’s manuscript) and is supported by King James usage; however, it is very possible that hand is an error for hands (the systematic usage for this type of expression elsewhere in the Book of Mormon).