We bring here the CBSE Class 10 Science SA-II Board Exam 2017 (Delhi): Marking Scheme that released by the board itself. This marking scheme has key answers (or values point) along with mark wise break up of every answer which gives better idea about the division of marks inside a question.
Importance of CBSE Class 10 Science Board Examination Marking Scheme:
Every year CBSE Board releases the marking scheme which was used while checking the answer booklets of CBSE Board Examinations. CBSE does this with a purpose of helping its students get an idea to frame a perfect answer that contains every important key point.
The word limit while answering questions of CBSE board examination is the most crucial factor. With the help of key answers in marking scheme, students will easily understand the criteria of word limit of answers to be written in CBSE Board Exams.
A few questions and their answers from CBSE Class 10 Science SA-II Board Exam 2017 (Delhi): Marking Scheme, are given below:
Q. Name the method by which spirogyra reproduces under favourable conditions. Is this method sexual or asexual? (1)
Q. An object is placed at a distance of 30 cm in front of a convex mirror of focal length 15 cm. Write four characteristics of the image formed by the mirror. (2)
Virtual, erect, diminished, laterally inverted (4 x ½ = 2)
Q. Two carbon compounds X and Y have the molecular formula C4H8 and C5H12 respectively. Which one of these is most likely to show addition reaction? Justify your answer. Also give the chemical equation to explain the process of addition reaction in this case. (2)
C4H8, it is an unsaturated hydrocarbon due to the presence of a double bond. (1+1)
Q. Write the names given to the vertical columns and horizontal rows in the Modern Periodic Table. How does the metallic character of elements vary on moving down a vertical column? How does the size of atomic radius vary on moving left to right in a horizontal row? Give reason in support of your answer in the above two cases. (3)
Vertical Columns – Groups (½ )
Horizontal Rows – Period (½ )
Metallic character increases (½)
Reason: Ability to lose electrons increases on moving down the group due to increase in distance between the nucleus and the valence electrons /decrease in the attraction between the nucleus and the valence electrons. (½)
Atomic radius decreases (½)
Reason: the nuclear charge increases on moving from left to right across a period resulting in increase in the attraction between the nucleus and the valence electrons. (½)
Q. What happens when:
(a) Accidently, Planaria gets cut into many pieces?
(b) Bryophyllum leaf falls on the wet soil?
(c) On maturation sporangia of Rhizopus bursts? (3)
(a) Each piece regenerates into new Planaria (1)
(b) Bud, at its notches develop into new plants. (1)
(c) It releases spores which germinate into new mycelium in moist conditions. (1)
Q. Due to gradual weakening of ciliary muscles and diminishing flexibility of the eye lens a certain defect of vision arises. Write the name of this defect. Name the type of lens required by such persons to improve the vision. Explain the structure and function of such a lens. (3)
Bifocal lens ½
Upper portion/ part
Click over the following links to get the complete CBSE Class 10 Science (Delhi) question paper and its marking scheme: