Date: 10/05/2022

Question Paper Code

31/2/1

Time: 2 Hrs.

Class-X

Max. Marks: 40

SCIENCE (Theory) Term-II (CBSE 2022)

GENERAL INSTRUCTIONS

Read the following instructions carefully and strictly follow them:

1. This question paper contains 15 questions. All questions are compulsory.
2. This question paper is divided into three Sections viz. Section A, B and C.
3. Section A – Question numbers 1 to 7 are short answer type questions. Each question carries two marks.
4. Section B – Question numbers 8 to 13 are also short answer type questions. Each question carries three marks.
5. Section C – Question numbers 14 and 15 are case based questions. Each question carries four marks.
6. Internal choices have been provided in some questions. Only one of the alternatives has to be attempted.

SECTION A

1. "Carbon prefers to share its valence electrons with other atoms of carbon or with atoms of other elements rather than gaining or losing the valence electrons in order to attain noble gas configuration." Give reasons to justify

this statement. [2]

Solution:

Carbon does not prefer to gain or lose electrons because:

On gaining four electrons it will form C^4- ion, which is highly unstable due to the large amount of energy required to overcome inter-electronic forces of repulsion. [1]

On losing four electrons it will form C⁴⁺ ion, which is highly unstable due to the large amount of energy required to remove four electrons from the carbon atoms. [1]

Therefore, in order to overcome these problems, carbon prefers to share its valence electrons with other atoms of carbon or with atoms of other elements.

1. The atomic number of an element 'X' is 11.
2. Write the electronic configurations of X and find its valency.
3. Write the formula and nature of its oxide. [2]

Solution:

K L М

<math>[\frac{1}{2}]</math>

1. Electronic configuration of 'X' = 2 8 1

Valency of 'X' = 1 <math>[\frac{1}{2}]</math>

1. Formula of oxide of 'X' = <math>X_2O</math> <math>[\frac{1}{2}]</math>

Nature of oxide of 'X' = Basic <math>[\frac{1}{2}]</math>

1. Give reasons:
2. Placenta is extremely essential for foetal development.
3. Uterine lining becomes thick and spongy after fertilisation. [2]

Solution:

1. Placenta is extremely essential for foetal development because of the following reasons:
2. The embryo gets nutrition from the mother's blood with the help of placenta. <math>[\frac{1}{2}]</math>
3. The developing embryo will also generate waste substances which can be removed by transferring them into the mother's blood through the placenta. <math>[\frac{1}{2}]</math>
4. Uterine lining becomes thick and spongy after fertilisation because it provides nurture and protection to the growing embryo. [1]
5. (a) Name the reproductive and non-reproductive parts of bread mould (Rhizopus).
6. List any two advantages of vegetative propagation. [2] Solution:
7. Sporangium and spores are the reproductive parts of bread mould (Rhizopus) while hyphae is a non- reproductive part of bread mould. [1]
8. Advantages of vegetative propagation:
9. Vegetative propagation helps in producing disease free plants.
10. All plants produced by vegetative propagation are genetically similar to the parent plants.
11. Vegetative propagation is usually a means of propagating plants which do not produce viable seeds.
12. Plants raised by vegetative propagation can bear flowers and fruits earlier than those which are produced from seeds. (Any two) <math>[2\times\frac{1}{2}]</math>