Using the following spontaneous reactions, classify the 3 metals involved (Cr, Sn, Al) according to increasing reductant properties.

a) 2Cr + 3Sn2+ 2Cr3+ + 3Sn
b) Al + Cr3+ Al3+ + Cr

To classify the metals according to increasing reductant properties, we need to determine which metal is more likely to be oxidized (acting as the reducing agent) and which is more likely to be reduced (acting as the oxidizing agent) in each reaction.

a) 2Cr + 3Sn2+ 2Cr3+ + 3Sn
In this reaction, chromium (Cr) is being oxidized from Cr to Cr3+, while tin (Sn) is being reduced from Sn2+ to Sn. The fact that chromium is being oxidized suggests that chromium has stronger reductant properties compared to tin. Therefore, tin (Sn) would have the least reductant properties, followed by chromium (Cr).

b) Al + Cr3+ Al3+ + Cr
In this reaction, aluminum (Al) is being oxidized from Al to Al3+, while chromium (Cr) is being reduced from Cr3+ to Cr. The fact that aluminum is being oxidized suggests that aluminum has stronger reductant properties compared to chromium. Therefore, chromium (Cr) would have the least reductant properties, and aluminum (Al) would have the strongest reductant properties.

Therefore, based on increasing reductant properties, the metals can be classified as follows:
1) Tin (Sn)
2) Chromium (Cr)
3) Aluminum (Al)

With no arrows how in the world do I know the reactants from the products?

Anyway, you know these are spontaneous reactions so you know Cr displaces Sn^2+ and Al displaces Cr^3+ so the series would be Al, Cr, Sn with the strongest reducing agent being at the top.