Question

(sif6)2- is known (sicl6)2- is not known

Answer 1

because in cs6 to it is known as it is ciaz ICL 6 means chlorine not fluoride that why it is not known

Answer 2

$\huge\boxed{\underline{\mathcal{\red{A}\green{N}\pink{S}\orange{W}\blue{E}\purple{R}}}}$

❤⭐MAIN REASONS:- ⭐❤

1. six lagre chloride ions cannot be accomodated around ${Si}^4+$ due to $\purple{\tt{Limitation}}$of its size.
2. Interaction between lone pair of chloride ion and${Si^4+}$ is not very strong.