Correct Answer:
(B)
H.C. Urey
Harold Clayton Urey, an American chemist discovered deuterium and heavy water in 1931. He was awarded Nobel Prize in Chemistry in 1934 for his discovery.
Ques:
22
Heavy water has molecular weight :
Correct Answer:
(B)
20
Heavy water (D2O), also called deuterium oxide, is water composed of deuterium, a hydrogen isotope with mass double that of ordinary hydrogen. Thus, heavy water has a molecular weight of about 20, whereas the ordinary water has a molecular weight of about 18.
Ques:
23
Consider the following statements :
Hard water is not suitable for
1. Drinking
2. Washing clothes with soap
3. Use in boilers
4. Irrigating crops
Which of these statements are correct ?
Correct Answer:
(D)
1, 2, 3 and 4
Hard water is described as 'hard' due to the presence of highly dissolved minerals specifically sulphates and chlorides of calcium and magnesium. Hard water is salty and therefore not used for drinking. It is very difficult to wash clothes with hard water as it requires more soap and leaves a messy scum that cannot be washed out easily. When hard water is boiled at home or in industries, it leaves deposits of magnesium salts. These deposits reduce the efficiency of boilers, kettles and pipes and can cause blockages and even burst of the boilers. If salt level increases in irrigation water, it becomes harder for lawns and landscape plant to take up water even though the soil is moist. Hard water blocks the Xylem tissues of the plants and thus not suitable for irrigation.
Ques:
24
The pH-value for water is –
Correct Answer:
(B)
Nearly 7
The pH value of pure water is 7. Pure water is neutral by nature. The solution with a pH less than 7 are said to be acidic and solutions with a pH greater than 7 are basic or alkaline.
Ques:
25
Which is the purest form of water?
Correct Answer:
(C)
Rainwater
Among the given options rainwater is the purest form of water. The water on the earth is mixed with alkaline and acidic materials that make the water impure.
Ques:
26
Assertion (A) : In the periodic table of chemical elements, electron affinity is always found to increase from top to bottom in a group.
Reason (R) : In a group, the atomic radii generally increase from top to bottom.
(a) Both
(A) and (R) are individually true, and (R) is the correct explanation of
(A).
(b) Both
(A) and (R) are individually true, but R is not the correct explanation of
(A).
Correct Answer:
(D)
is false but (R) is true.
In the periodic table of chemical elements, the electron affinity decreases down the group but increases up for the group and from left to right across periods of a periodic table because the electron added to energy levels become closer to the nucleus, thus a stronger attraction between the nucleus and its electrons. An atom gets larger as the number of electronic shells increases. Therefore, the radius of atoms increases as you go down a certain group in the periodic table of elements. However, the size of an atom will decrease as you move from left to right of a certain period. Thus, Assertion (A) is false, while Reason (R) is true.
Ques:
27
Which of the following is a fundamental element :
Correct Answer:
(B)
Diamond
Chemically diamond is the purest form of Carbon (crystal structure). Hence, it is a fundamental element. Sand is basically made up of Silicon and Oxygen, Marble is made up of Calcium, Carbon and Oxygen while sugar is mainly the compound of Carbon, Hydrogen and Oxygen.
Ques:
28
Which of the following is the most common element in the Universe?
Correct Answer:
(A)
Hydrogen
The most abundant element in the Universe is Hydrogen, which makes up about 3/4 of all matter. Helium makes up most of the remaining 1/4. Thus, it is clear that hydrogen is the most common and abundant element in the Universe. While the most abundant element in the earth's crust is Oxygen making up 46.6% of earth crust.
Ques:
29
Which is the most abundant element after Oxygen?
Correct Answer:
(A)
Silicon
The most abundant element on earth's surface after Oxygen is Silicon. It was discovered by J.J. Berzelius in 1824. The word 'Silicon' was taken from the Latin word silex. Silicon chips are used as a semiconductor in computers.
Ques:
30
The element found maximum in the soil layer is –
Correct Answer:
(A)
Oxygen
The element found the maximum in the soil layer is Oxygen 46.60% followed by Silicon 27.72%, Aluminium 8.13%, Iron 5.00% and Calcium 3.65%.