The s and p sublevels of an atom of an element in period 3 are filled with electrons. which orbitals are filled in this atom?

1s,2s,2p,3s,3p

Explanation:

If an element is in period 3, then it has three energy levels. For the 3s and 3p orbitals to be filled, then the inner orbitals must have been filled before. That is 1s, 2s,2p, are all previously filled with electrons before the valence shells, 3s and 3p are filled. Hence all together, the filled orbitals are; 1s,2s,2p,3s,3p.

2h2o2--> 2h2o + o2

this reaction is of the spontaneous decomposition of hydrogen peroxide down into water and oxygen.

add 2 molecules of hydrogen peroxide and 2 molecules of water. since oxygen is naturally diatomic, the total number of atoms of each element is now the same on both sides of the equation so it is balanced.

this may not be entirely correct but let me know.