Ziegler Natta catalyst is
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → \(TiCl_4 + Al(CH_3)_3\)
A Ziegler-Natta catalyst is a combination of titanium tetrachloride (\( \ce{TiCl4} \)) with a trialkylaluminium, usually triethylaluminium, \( \ce{Al(C2H5)3} \). It is used to make high density polythene (HDP): ethene is polymerised in a hydrocarbon solvent at 333–343 K and a pressure of only 6–7 atmospheres.
\( \displaystyle n\,\ce{CH2=CH2} \xrightarrow[333-343\ \mathrm{K},\ 6-7\ \mathrm{atm}]{\ce{TiCl4 + AlR3}} \ce{-(CH2-CH2)_{n}-} \)
The polythene formed consists of linear chains that pack closely, so it is denser, tougher and harder than the branched low density polythene made by the free radical method. Among the options, only TiCl4 + Al(CH3)3 is a titanium chloride–alkylaluminium pair.
Note: This question is from the pre-rationalised NCERT book (2022-23). The topic is not there in the latest NCERT book (2026-27), and it is also out of the CUET 2026 syllabus.
NCERT (Pre-rationalised edition, 2022-23):
High Density Polythene
