In which group of the periodic table do most of the elements exhibit both positive and negative oxidation states?
a. 17
b. 2
c. 12
d. 7

The answer is:

A. 17

The explanation:

first we have to define the oxidation state:

It is the loss of the electrons in the atom of the component , or the amount of the oxidation or the degree of the oxidation of an atom.

and the group 17 consist of Halogens:

1- Fluorine : with atomic number 9 , The oxidation state of it is always -1 but in its diatomic case the oxidation state is zero.

2- chlorine: Cl with atomic number 17 , The oxidation states of it are multiple oxidation states for example -1, +1, 3, 5, and 7.

3- Bromine: Br with atomic number 35 , The oxidation states of it are -1, +1, 3, 4 and 5.

4- Iodine: I with atomic number 53 , The oxidation states of it  are oxidation states -1, +1, 5 and 7

5- Astatine: At with atomic number 85, The oxidation states of it are -1, +1, 3, 5 and 7

So this group (17) exhibit both positive and negative oxidation states.

rosa was looking for patterns to predict the products of chemical reactions. she recorded three similar decomposition reactions in the table.she should record 2licl + 3o2.

in the last row of the table. it is the thermal decomposition of chlorate lithium, hence, she should record these products as: lithium chloride ( 2licl ) and oxygen ( 3o2 )   2 > 2 licl + 3o2.