Fill in the blanks by choosing the appropriate word/words from those given in the bracket:
(vacant, square planar, tetrahedral, 64%, crystal, decreases, efficient, increases, 74%, `sp^(3)d^(2), sp^(3)`)
Electrons trapped in the ......... sites of the......... lattice are called F-centres.

Explanation

To solve the question, we need to fill in the blanks with the appropriate words from the options provided. The statement we need to complete is:

"Electrons trapped in the ________ sites of the ________ lattice are called F-centres."

Let's analyze the options:

1. **First Blank**: We need a word that describes the type of sites where electrons are trapped. The options are:
- vacant
...