Adding borax to PVA

By Frome CC Science

What happens when you add food colouring, then some borax to PVA glue?

 

Question

Why does the PVA become gloopy?

Answers

(a) The PVA molecules become longer
(b) The PVA molecules form side chains
(c) Cross links are formed between the PVA molecules
(d) The PVA molecules are broken up