Which of the following can be made into crystal?

A crystalline solid AB has NaCl type structure with radius of B^(-) ion is 250 pm. Which of the following cation can be made to slip into tetrahedral site of crystals of A^(+)B^(-) ?

A crystalline solid AB has NaCl type structure with radius of B^(-) ion is 250 pm. Which of the following cation can be made to slip into tetrahedral site of crystals of A^(+)B^(-) ?

Which of the following best defines a crystal ?

Which of the following is a covalent crystal?

Which of the following polymers can be made by cationic addition polymersation mechanism?

Which of the following polymers can be made by cationic addition polymersation mechanism?

Which of the following can not be made by reduction of ketone or aldenhyde with NaBH_4 ?