21.

Which of the following compounds is expected to be optically active ?

• (CH₃)₂CHCHO

• CH₃CH₂CH₂CHO

• CH₃CH₂CHBrCHO

• CH₃CH₂CBr₂CHO

Which one of the following is a second order reaction ?

• H₂ + Br₂ $\to$ 2HBr

• NH₄NO₃ $\to$ N₂ + 3H₂O

• H₂ + Cl₂ $\stackrel{\mathrm{Sunlight}}{\to }$ 2HCl

• CH₃COOCH₃ + NaOH $\to$ CH₃COONa + CH₃OH

Formation of coloured solution is possible when metal ion in the compound contains :

• paired electrons

• lone pair of electrons

• unpaired electrons

• None of the above

In the periodic table metals usually used as catalysts belong to :

• f - block

• d - block

• p - block

• s - block

In a neutron induced reaction of ${}_{92}{}^{235}\mathrm{U}$ , the product obtained is ${}_{37}{}^{95}\mathrm{Rb}$ , three neutrons and an element (new nuclide) .The other new nuclide is :

• ${}_{55}{}^{138}\mathrm{Cs}$

• ${}_{56}{}^{140}\mathrm{Ba}$

• ${}_{54}{}^{144}\mathrm{Xe}$

• ${}_{38}{}^{90}\mathrm{Sr}$

The electronic configuration of Cr³⁺ is :

• [Ar] 3d⁴ 4s²

• [Ar] 3d³ 4s⁰

• [Ar] 3d² 4s¹

• [Ar] 3d⁵ 4s¹

The lanthanide contraction is responsible for the fact that :

• Zr and Zn have the same oxidation state

• Zr arid Hf have about the same radius

• Zr and Nb have similar oxidation state

• Zr and Y have about the same radius

Which of the following forms a colourless solution in aqueous medium ?

• Cr³⁺

• V³⁺

• Sc³⁺

• Ti³⁺

When a sulphur sol is evaporated sulphur is obtained .On mixing with water sulphur sol is not formed .The sol is :

• lyophilic

• reversible

• hydrophobic

• hydrophilic

Important ore of zinc is :

• calamine

• cryolite

• zinc blende

• malachite