What alkali and alkaline earth metal oxides will turn moist red litmus blue and finally white? How many of the following will turn moist red litmus blue and finally white?
$\ce{Li2O}$, $\ce{KO3}$, $\ce{RbO2}$, $\ce{Cs2O2}$, $\ce{BeO}$, $\ce{MgO}$, $\ce{BaO2}$, $\ce{SrO}$.

Since bleach convert moist red litmus blue and then white, but how we can identify which compound will act as bleach ?
The standard oxides $\ce{Li2O, MgO}$ and $\ce{SrO}$ are water soluble and hydrolyse to form hydroxides and a basic solution. $\ce{BeO}$ is insoluble in water.

$\ce{RbO2}$ is a superoxide which in aqueous solution undergoes disproportionation to $\ce{O2}$ and $\ce{OH-}$ so will give a blue litmus test. 

The peroxides $\ce{Cs2O2}$ and $\ce{BaO2}$ react with water to give hydrogen peroxide and the hydroxides, so again a basic solution(source). The hydrogen peroxide produced will bleach the litmus paper.

$\ce{KO3}$(Potassium Ozonide) is highly unstable, decomposes in water to $\ce{O2}$ and $\ce{KOH}$

The oxides which will NOT decolorize litmus are $\ce{Li2O, MgO, BeO}$ and $\ce{SrO}$. The peroxides ($\ce{Cs2O2}$ and $\ce{BaO2}$), the superoxide($\ce{RbO2}$) and the ozonide($\ce{KO3}$) will decolorize litmus.