what is oxidized? what is reduced?

[arleshea]

2Cs (s) + F₂ (g) -> 2CsF (s)

[soma]

Fluorine is negative compared to cesium. Fluorine gives electrons to cesium. Cesium's positive charge is reduced, fluorine is oxidized.

[KriggY]

Fluorine is negative compared to cesium. Fluorine gives electrons to cesium. Cesium's positive charge is reduced, fluorine is oxidized.

im sorry you are wrong.
Oxidation is giving electrons away not taking them.
Fluorine has electronegativity around 4.0 and cessium around 0.7, its not possible for cessium to take away electrons from fluorine.(F is the most electronegative elemnet, Cessium with Francium are the least electronegative elements)
F(-) means that fluorine has 1 more electron compared to ground state (electrons have negative charge, therefore its - not +)
So:
Fluorine is oxidizing agent and is REDUCED (hint: ground state is alway 0, if atom takes electrons its oxidation number decrease, is reduced=reduction)
Cessium is reducing agent and is OXIDIZED

[GrahamKemp]

The choice of the word "reduction" is an unfortunate historic happenstance. It confuses many. It originally referred to a reduction of weight when smelting an ore (due to loss of oxygen).

However, reactions with oxygen are a special case of a more general class of reactions. "Oxidization" has been redefined in terms of electric charge transfer. The term "reduction" was kept in use, but counterintuitively redefined as a gain of electrons. (Or, more intuitively, a reduction of the oxygenation number.)

Remember: "OIL RIG" → Oxidation Is Loss of electrons, Reduction Is Gain of electrons

2Cs (s) + F₂ (g) -> 2CsF (s)

Look at the Half Reactions.
Oxidation : 2 Cs → 2 Cs⁺ + 2 {e-}
Reduction: F2 + 2{e-} → 2 F^-