Which of the following processes occur during fractional distillation of petroleum?
Condensation and diffusion
Diffusion and evaporation
Diffusion and sublimation
Evaporation and condensation
Correct answer is D
Fractional distillation is a series of processes of evaporation and condensation at a number of points in a vertical column.
Which of the following oxides is amphoteric?
Carbon(II) oxide
Nitrogen(IV) oxide
Lead(II) oxide
Calcium oxide
Correct answer is C
Aluminium oxide is an amphoteric oxide. With sodium hydroxide solution, it produces water and sodium aluminate (NaAlO2). The other common examples of amphoteric oxides include SnO, ZnO, and PbO. Al2O3 is an amphoteric oxide.
| Substitute | Meltig point / ºC | Boiling point / ºC |
| P | - 78 | -25 |
| Q | - 8 | 40 |
| R | - 6 | 150 |
| S | 44 | 280 |
Which of the substances is a liquid at room temperature and rapidly evaporates on exposure to air?
P
Q
R
S
Correct answer is B
Q has slightly lower boiling point which when expose to air may evaporate rapidly.
Electropositivity of elements across the periodic table normally
remains constant down the group
Increases across the period
decreases across the period
decreases down the group
Correct answer is C
Electropositivity is known to increase down groups and decrease across periods in the modern periodic table (i.e., electropositivity decreases from left to right and it increases from up to down).
period 4, p- block
period 3, p- block
period 4, d- block
period 3, d- block
Correct answer is A
Selenium is a chemical element with the symbol Se and atomic number 34. It is a non-metal