Class X (CBSE 2019) Science Delhi (Set-2)

General Instructions:

1. The question paper comprises five sections, A, B, C, D and E. You are to attempt all the sections.
2. All questions are compulsory.
3. Internal choice is given in sections B, C, D and E.
4. Question numbers 1 and 2 in Section A are one mark questions. They are to be answered in one word or in one sentence.
5. Question numbers 3 to 5 in Section B are two-marks questions. These are to be answered in about 30 words each.
6. Question numbers 6 to 15 in Section C are three-marks questions. These are to be answered in about 50 words each.
7. Question numbers 16 to 21 in Section D are five-marks questions. These are to be answered in about 70 words each.
8. Question numbers 22 to 27 in Section E are based on practical skills. Each question is a two marks question. These are to be answered in brief.

Question 1

Name and define the SI unit of current.

SOLUTION:

The SI unit of current is ampere. One ampere is defined as the current produced at a point through which, 1 Coulomb of charge passes in 1 second or flow of one coulomb of charge in one second through a point.

Question 2

Write the name of the main constituent of Biogas. Also, state its percentage.

SOLUTION:

The main constituents of biogas are Methane and Carbon dioxide and their percentage is as follows:

1) Methane is 75%

1. Carbon Dioxide is 23%

Other gases are approximately 2%

Question 3

Write the name, symbol and electronic configuration of an element X whose atomic number is 11.

OR

Can the following groups of elements be classified as Dobereiner's triad:

(a) Na, Si, Cl (b) Be, Mg, Ca

Atomic mass of Be-9, Na-23, Mg-24, Si-28, Cl-35, Ca-40.

Justify your answer in each case.

SOLUTION:

The element X with atomic number 11 is Sodium with symbol Na. Electronic configuration of the element is 2,8,1.

OR

According to Dobereiner's traid, the atomic mass of the second element is nearly equal to the average of the atomic masses of the first and the third elements provided the three elements are arranged in the increasing order of their atomic masses.

(a) Na, Si, Cl

Atomic mass of Na-23, Si-28, Cl-35

Average of atomic masses of Na and CI <math>\frac{23+35}{2} = 29</math>, which is nearly equal to the

atomic mass of Si i.e. 28.

Thus, it can be considered as Dobereiner's triad.

(b) Be, Mg, Ca Atomic mass of Be-9, Mg-24, Ca-40

Average of atomic masses of Be and Ca <math>\frac{9+40}{2} = 24.5</math> which is nearly equal to the atomic mass of Mg i.e. 24.

Thus, it can be considered as Dobereiner's triad.

Question 4