Answer: oxygen
There is the s,p,d and f blocks, from groups 1-2 that is the s block, 13-18 that’s the p block, 3-12 is the d block and the f would be lanthanide(#57-71) and actinide (#89-103).
I’m pretty sure it’s sulphur dioxide
The reason for adding a limited amount and then an excess amount is that initially a metal hydroxide may form which becomes soluble when more base is added and the metal complex forms.
In qualitative analysis is a common to add the base in drops and then in excess. When added in drops, the metal hydroxide is formed. This metal hydroxide is often insoluble.
After this metal hydroxide is formed, the base could be added in excess such that the metal hydroxide dissolves in the excess base by forming a complex.
For instance;
CuCl2(aq) + 2NaOH(aq) -------> Cu(OH)2(s) + 2NaCl(aq)
Cu(OH)2(s) + 2OH^-(aq) -------> [Cu(OH)4]^2+(aq)
Learn more: brainly.com/question/1527403
