CBSE Guess > Papers > Question Papers > Class X > 2009 > Science > Science
 
SCIENCE - 2009
Comptt
Set- III - (Delhi)
Time allowed : 2 1/2 hours
Maximum marks : 60
General Instructions :
(i) The question paper comprises of two Sections, A and B. You are to attempt both
the Sections.
(ii) All questions are compulsory.
(iii) There is no overall choice. However, internal choice has been provided in all the
three questions of five marks category. Only one option in such questions is to be
attempted.
(iv) All questions of Section A and all questions of Section B are to be attempted
separately.
(v) Questions number 1 to 6 in Section A and 17 to 19 in Section B are short answer
type questions. These questions carry one mark each.
(vi) Questions number 7 to 10 in Section A and 20 to 24 in Section B are short answer
type questions and carry two marks each.
(vii) Questions number 11 to 14 in Section A and 25 and 26 in Section B are also short
answer type questions and carry three marks each.
(viii) Questions number 15 and 16 in Section A and question number 27 in Section B
are long answer type questions and carry five marks each.
Section A
Q. 1. Calcium, Strontium and Barium form a Dobereiner’s triad. The atomic masses of Calcium and Barium are 40 and 137 respectively. Predict the atomic mass of Strontium. 1
Ans.
| Element of the triad |
Symbol |
Atomic masses |
| Calcium |
Ca |
40 |
| Strontium |
Sr |
? |
| Barium |
Ba |
137 |
According to Dobereiner’s triad, atomic mass of Strontium is the arithmetic mean of Ca and Ba.
Atomic mass of Sr 
|
