Science: 2017: CBSE: [Delhi]: Set – II

The molecular formula of first member is CH₃Br and the molecular formula of second member is C₂H₅Br

Planariareproduces by regeneration. It is a type of asexual reproduction. In asexual reproduction, the planarian detaches its tail end and each half regrows the lost parts. If a Planaria is cut into two halves, both halves may become two new Planaria.

A forest ecosystem is a natural ecosystem consisting of biotic components-all plants, animals and micro-organismsin in that area functioning together with abiotic components-all of the non-living physical factors of the environment.

It is given that the object is placed somewhere between the pole and infinity. The ray diagram for the given case is as shown below:

Four characteristics of the image formed by the mirror are:

(i) The image is formed behind the mirror.

(ii) The image formed is virtual.

(iii) The image formed is erect.

(iv) The image formed is diminished.

Sustainable management of natural resources is necessary because:

i. It helps in the conservation of a replenishable resource, which otherwise may get depleted soon.

ii. Depletion of one resource may affect other resources also.

iii. It also prevents pollution and maintains our ecosystem.

Re-use strategy is better than recycling because:

i. Recycling uses some energy.

ii. Recycling needs segregation of wastes.

Active participation of local people to save forests is an activity towards the conservation of forests. There are many examples, which suggest that involvement of local communities is necessary for any conservation effort. The Bishnoi community of Rajasthan is one such example. Amrita Devi Bishnoi is still remembered with reverence for the way she fought for protecting the khejri trees in Khejrali village. In 1731, she along with 363 other people sacrificed her life for the protection of khejri trees.

The general formula of alkenes is C_nH_2n. Therefore, the molecular formula C₃H₆ represents an alkene.

The general formula of alkanes is C_nH_2n+2. Therefore, the molecular formula C₄H₁₀ represents an alkane.

Alkane is a saturated hydrocarbon whereas alkene is an unsaturated hydrocarbon. Since, addition reactions are characteristic of alkenes. Therefore, C₃H₆ is likely to show addition reactions. The reaction in which an unsaturated hydrocarbon combines with another substance to give a single product is called an addition reaction. It is a characteristic property of unsaturated hydrocarbons (alkenes and alkynes).

The unsaturated compounds have multiple bonds. During the addition reactions, the addition takes place at multiple bond and new single bonds are formed.

(i) Positions in Periodic Table:

Electronic configuration of element with atomic number 20 is 2, 8, 8, 2. According to its configuration, P belongs to 2^nd group because it has 2 electrons in its outermost shell and 4^th period of the modern periodic table as the element is of N electronic shell.

On the other hand, electronic configuration of element ‘Q’ with atomic number 17 is 2, 8, 7. According to its configuration, Q belongs to 17^th group because it has 7 electrons in its outermost shell and 3^rd period of the modern periodic table as the element is of M electronic shell.

(ii) Molecular formula of compound formed:

Atomic number of P = 20
Electronic configuration of P = 2,8,8,2
Number of valence electrons of P = 2
Valency of P = 2

Atomic number of Q= 17
Electronic configuration of Q = 2,8,7
Number of valence electrons of Q = 7
Valency of Q = 8 - 7 = 1
Therefore the formula of the compound formed is PQ₂.

Modern Periodic Table has 18 vertical columns known as ‘Group’ and 7 horizontal rows are known as ‘Period’.

(a) On moving down in a vertical column metallic character increases because on moving down in a group atomic size increases due to addition of a new shell, therefore, it can easily lose electrons from its valence shell.

(b) On moving left to right in a horizontal row atomic size decreases because nuclear charge on valence shell electrons increases.