Three elements 'X', 'Y' and 'Z' have atomic numbers 7, 8 and 9 respectively. |
(a) State their positions (Group number and period number both) in the Modern Periodic Table. |
(b) Arrange these elements in the decreasing order of their atomic radii. |
(c) Write the formula of the compound formed when 'X' combines with 'Z'. |
With the help of an example justify the following statement: |
"A trait may be inherited, but may not be expressed." |
(a) Define focal length of a spherical lens. |
(b) A divergent lens has a focal length of 30 cm. At what distance should an object of height 5 cm from the optical centre of the lens be placed so that its image is formed 15 cm away from the lens? Find the size of the image also. |
(c) Draw a ray diagram to show the formation of image in the above situation. |
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