Explore topic-wise InterviewSolutions in Current Affairs.

Weight can be expressed completely only when magnitude and direction are both given so weight is a vector quantity.

i. weight

ii. vector

iii. metric system

iv. cubit

v. gun

1. Gravitational power of moon is less than the earth.

2. Weight depends on the gravitational power of that place.

3. Since the gravitational power of the moon is less than that of the earth, the weight on moon is less than that on the earth.

i. True

ii. False. 

Unit of mass in C.G.S. system is gram

iii. False. 

Symbol of unit of second is ‘s’

iv. False. 

1 cubic foot means 28.317 litres.

v. False. 

Vector quantity required magnitude and direction both.

Following precautions will be taken to make accurate measurements in day to day affairs:

1. The balance should carry the stamp of standardisation by the department of weights and measures. 

2. Balance should be stable and the pointer of the balance should be upright. 

3. The underside of the pan should not be tampered with any other weight or layers of other metal. 

4. The weight should be made of metal.

It is necessary to get the weights and measures standardized at regular intervals because of that accurate weight and measurement can be taken. Errors will be avoided.

The quantity that is expressed completely only.’ v when magnitude and direction are both given is called a vector quantity. Displacement, velocity are vector quantities e.g. a displacement of 20 km towards north, the aeroplane flying at a velocity of 500 km/hr towards Mumbai.

A quantity that can be completely expressed by its magnitude alone is called a scalar quantity, e.g. length, breadth, area, mass, temperature, density, time, work. In all these examples a value with a unit is used to express quantities. Thus, we say that the length of a tunnel is 2 km.

Major causes of errors in measurement are:

1. Not using the appropriate device. 

2. Not using the device properly.

Example: While buying things at grocery shops and the vegetable market remember to look out for the following:

• The balance should carry the stamp of standardisation by the department of weights and measures.
• Balance should be stable. The pointer of the balance should be upright.
• No changes should be done on the underside of the pan of the balance.
• Weight should be made up of metals and it has to be standardized.

i. mass

ii. mass

iii. greater

iv. scalar

v. mass

1. Measurement of substances that are precious or of great importance and used in very small quantities is done meticulously and accurately.

2. Due to advancements in technology, devices that measure very small magnitudes of quantities like distance, mass, time and temperature are available now.

3. e.g. distance and time in connection with very important sports competitions, mass of gold, body temperature etc.

4. Devices to be used for this are thermometer, digital balance (Analytical balance) etc.

It is not proper to measure quantities by using body parts as units because length of the body parts changes from person to person, so accurate measurement can not be found with the body parts as units.

1. The gravitational force that acts on the mass is called the weight.

2. The earth is not exactly spherical, it flattens at the poles. 

3. As the distance increases the gravitational force decreases. 

4. Therefore due to reduced distance at the poles compared to the equator, the weight is maximum at the poles than equator.

An extremely accurate type of clock which is regulated by the vibrations of an atomic or molecular system such as caesium atom or ammonia is called atomic clock. It is used to maintain standard times of countries accurately.

i. True

ii. True

iii. False. 

Weight and mass are both different quantities

iv. False. 

Work is a scalar quantity

v. False.

 Velocity is a vector quantity

(i) True.

(ii) True.

(iii) False. (The number of electrons in a given orbit is given by the formula 2n2)

(iv) True.

(v) False. (The chemical properties of isotopes are the same.)

Correct option is (c) bromine

Correct option is (d) chlorine

Correct option is (d) 18

Correct option is (b) 32

Correct option is (c) 18

(i) False. (The maximum capacity of the N shell is 32 electrons.)

(ii) True.

(iii) True.

(iv) True.

(v) False. (Electrons moving in different orbits possess different amounts of energy.

The maximum capacity of the M shell is 18 electrons.

a. A : Rough, nonvirulent R-strain B : Heatkilled virulent S-strain 

b. When DNA of heat-killed S-strain bacteria is treated with DNase, mouse remains alive as transformation does not take place. This proves that DNA is the genetic material.

(1) A : Circular, unfolded chromosome 

b : Folded chromosome (40 to 50 loops) 

c : Supercoiled, folded chromosome 

(2) (A) 350 µ (B) 30 µ (C) 2 µ

(i) Chromosome no. 1 - 2968 genes 

(ii) Y chromosomes - 231 gene

a. A : Smooth strain (III-S) B : Rough Strain and Heat-killed Smooth Strain 

b. F. Griffith conducted the experiment shown in the diagram.

Infection B : Blending C : Centrifugation Scientists who carried out experiment are Alfred Hershey and Martha Chase.

(i) Chromosome-1

(ii) Y-Chromosome

a. Ammonium chloride (NH4Cl). 

b. To check if DNA replication was semi-conservative. 

c. The heavy and light DNA molecules were distinguished by centrifugation in a cesium chloride density gradient. 

d. The scientists concluded that DNA replicates semi-conservatively.

a. Chromosome 1 has most genes and the Y has the fewest gene. 

b. The information regarding the occurrence of 1.4 million SNPs (single nucleotide polymorphism) revolutionise the processes of finding chromosomal locations for diseaseassociated sequences and tracing human ancestory (history).

The number of electron in the extranuclear part is equal to the number of protons, i.e. atomic number. The atomic number of sodium is 11.

Correct option is (a) 1800

The atomic number of carbon, i.e. the proton number of carbon is 6. 

The number of electron in the extranuclear part is equal to the number of protons in the nucleus. 

∴ The number of electrons in a carbon atom = 6.

The total number of protons and neutrons in the nucleus of the atom is called the atomic mass number. The atomic number, i.e. the proton number of carbon is 6 and the mass number is total number of protons and neutrons in the carbon, i.e. 6 protons + 6 neutrons = 12. Therefore, the atomic number and mass number of carbon are 6 and 12 respectively.

Valency: The capacity of an ; element to combine with another element is known as valency. Valence electrons: The electrons in the outermost shell of an atom of an element are called valence electrons. 

Helium and neon, atoms of both these gaseous element do not combine with any other atom. These elements are chemically inert, i.e. their valency is zero.

Helium atom contains two electrons, indicates that the outermost shell of helium has an electron duplet. The valence shell of neon is completely filled, i.e. neon has an electron octet. Similarly argon contains eight electrons in the valence shell, i.e. argon has an electron octet. It is confirmed that the valency is zero when electron octet (or duplet) is complete.

Atoms of all the elements except inert gases have tendency to combine with other atoms, i.e. they have a non zero valency. The molecules formed by combination with hydrogen (E.g. H , HCl) that valency of hydrogen is one. The electronic configuration of hydrogen shows that there is one electron less than the complete duplet state. This number ‘one’ matches with the valency of hydrogen which is also one.

It means that there is relationship between the valency of an element and the number of electrons in its valence shell.

Paper, plywood, matches, resins and lac.

Atomic number : 

Atomic number is the number of protons in the nucleus of an atom, denoted by ‘Z’.

• F is the symbol of element (Fluorine). 
• 9 is the atomic number. 
• 19 is the mass number. 
• Hence fluorine has 9 protons and (19 – 9 = 10) 10 neutrons in its nucleus. 
• 9 electrons are revolving around the nucleus.

An atom is the smallest particle of an element which retains its chemical identity in all physical and chemical changes.

An atom can achieve an octet by two ways. 

1.  One by transfer of electrons. 
2.  Other by sharing of electrons. 
3.  Both the processes results in the formation of bonds between atoms.

Magnesium : 

a) Atomic number of magnesium is 12. 

b) Distribution of electrons is 2, 8, 2. 

c) Hence the valency is 2. 

Sodium : 

a) Atomic number of sodium is 11. 

b) Distribution of electrons is 2, 8, 1. 

c) Hence the valency is 1.

Valency: 

The number of electrons present in outer most orbit of an atom is called its valency. 

Valency of Nitrogen : 

a) Atomic number of nitrogen is 7. 

b) The distribution of electrons is 2, 5. 

c) The outer most orbit has 5 electrons. 

d) Hence its valency should be 5. But it is easier to nitrogen to gain 3 electrons than to loose 5 electrons for becoming octet. 

e) Hence the valency of nitrogen is ‘3’.

Valency of Boron : 

a) Atomic number of boron is 5. 

b) The distribution of electrons is 2, 3. 

c) The outer most orbit has 3 electrons. 

d) Hence the valency of boron is 3.

Atoms of the same element having the same atomic number, but different atomic mass numbers are called isotopes.

a) Atomic number of sulphur is 16. 

b) The distribution of electrons is 2, 8, 6. 

c) Hence the valency should be ’6′. 

d) But it is easier to sulphur to gain 2 electrons than loosing 6 electrons to become octet. Hence its valency would become 2. 

e) So, sulphur shows multiple valency, i.e., ‘2’ or ‘6’.