Science: 2017: CBSE: [All India]: Set – II

The molecular formulas of 2^nd and 3^rd member of this series are C₃H₄ (propyne) and C₄H₆ (butyne) respectively.

During replication, most of the base sequences in new copies are identical to the parent DNA. However, some changes occur either due to mutations or due to minor errors during replication process. Therefore, newly formed DNA copies may not be identical at times.

According to 10% law, in a food chain, only 10% of the total energy is transferred to the next topic level.

Since, rats have 500 J of energy,

10% of 500 J =50 J

Thus, the snakes have received 50 J of energy from the rats.

Similarly, snakes have 50 J of energy and,

10% of 50 J = 5 J

Thus, the energy available to the hawks is 5 J.

 Given that the object is placed at a distance 30 cm from lens which means that the object is placed between the optical centre and infinity. The ray diagram for the given case is as follows:

Four characteristics of the image formed are,

(i) The image is formed on the same side as that of the object.

(ii) The image formed is virtual.

(iii) The image formed is erect.

(iv) The image formed is diminished.

i) Equitable distribution of resources is essential so that every individual gets an equal right to access all the available resources and is benefited directly or indirectly.

The two forces which are against such distributions are:

a) lack of natural resources

b) profit motto by people exploiting resources

We must conserve our forests because:

a) Forests are rich in flora and fauna and provide home to many species.

b) Forests protect the land from erosion.

The two factors responsible for causing deforestation are:

a) Urbanisation

b) Forest Fires

Number of periods in modern periodic table=7

Number of groups in modern periodic table=18

(i) Metallic character of elements decreases from left to right in a period. This is because tendency of an element to lose electrons decreases as we move from left to right.

(ii)Metallic character of elements increases as we move down the group. This is because tendency of an element to lose electrons increases as we move down the group.

(a)Valency of Na = 1

Valency of Mg = 2

Valency of Al = 3

Among these, Al has highest valency of 3.

(b) Electronic configuration of Na – 2,8,1

Electronic configuration of Mg – 2,8,2

Electronic configuration of Al – 2,8,3

Elements Na, Mg and Al belong to the 3^rd period of the modern periodic table. On moving from left to right in the period (Na to Al), atomic size decreases because outer electrons are added to the same valence shell and effective nuclear charge increases.

Therefore, Na has the largest atomic size.

(c) Na has the maximum reactivity.

This is because Na has to lose only one electron from its valence shell to acquire noble gas configuration whereas Mg and Al have to lose 2 and 3 valence electrons respectively which requires more energy.