How many equivalents are in 0.40 mole of #K^+#?
In the context of ions, an equivalent can be thought of as the number of moles of monovalent ions needed to neutralize the charge of an ion of opposite charge.
In your example, you're dealing with a potassium cation,
Since a charge of
Therefore, you will have
#0.40 color(red)(cancel(color(black)("moles K"^(+)))) * "1 Eq"/(1color(red)(cancel(color(black)("mole K"^(+))))) = color(green)(|bar(ul(color(white)(a/a)color(black)("0.40 Eq")color(white)(a/a)|)))#
A quick way to remember how this works -- the number of equivalents of a given ion in solution is calculated using the number of moles and the valence of said ion.
#color(blue)(|bar(ul(color(white)(a/a)"no. of Eq" = "no. of moles" xx "valence"color(white)(a/a)|)))#
For example, one mole of a
#"no. of Eq" = "1 mole" xx color(red)(2) = "2 Eq"#
in solution. This is the same as saying that you need