All India Engineering / Architecture Entrance Examination (AIEEE)

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AIEEE 2007 Chemistry

Q. 19. A radioactive element gets spilled over the floor of a room. Its half–life period is 30 days. If the initial activity is ten times the permissible value, after how many days will it be safe to enter the room?

1. 1000 days
2. 300 days
3. 10 days
4. 100 days

Sol: Let the permissible activity limit of the radioactive element be x, then the initial activity would be 10 x.

Correct choice: (4)

Q. 20. Which one of the following conformations of cyclohexane is chiral?

1. Twist boat
2. Rigid
3. Chair
4. Boat

Sol: Twist boat conformation of cyclohexane is chiral because it has neither plane of symmetry nor centre of symmetry. Correct choice: (1)

Q. 21. Which of the following is the correct order of decreasing SN₂ reactivity?

1. RCH₂X > R₃CX > R₂CHX
2. RCH₂X > R₂CHX > R₃CX
3. R₃CX > R₂CHX > RCH₂X
4. R₂CHX > R₃CX > RCH₂X
   (X = a halogen)

Sol: The reactivity of a compound towards SN₂ reaction decreases as the crowding at the C–atom containing leaving group increases. Correct choice: (2)

Q. 22. In a following sequence of reactions,

1. butanal
2. n–butyl alcohol
3. n–propyl alcohol
4. propanal

Sol:

Correct choice: (3)