It would protect best against C) Alpha radiation, as Beta radiation is stopped by lighter metals such as aluminium, and Gamma radiation can only be stopped by heavier metals such as lead.
O2 isn't necessary for rusting, but some source of oxygen is required. Rust is just another name for iron oxide, and without oxygen there can't be oxide.
Hope this helps,
Davinia.
Another name for a mesh screen is a sieve.
