1. Q21 Name a non-metal which is lustrous and a metal which is non-lustrous.
  2. Q22 What is the pH value of salt formed by a weak acid and strong base?
  3. Q23 Name the chambers of the human heart.
  4. Q24 Write the number of periods the modern periodic table has. How do the valency and metallic character of elements vary on moving from left to right in a period? How do the valency and atomic size of elements vary down a group?
  5. Q25 How do desert plants perform the photosynthesis process as their stomata remain closed during daytime?
  6. Q26 The nature of image formed by a convex mirror when the object distance from the mirror is less than the distance between pole and focal point (F) of the mirror would be
  7. Q27 Why do we not see the actual depth of a lake?
  8. Q28 On the basis of electronic configuration, how will you identify the first and the last element of a period?
  9. Q29 Read the given passage and answer the questions that follow: Elements are arranged in the Modern Periodic table in increasing order of their atomic numbers. Metals are on the left hand side and middle of the periodic table mainly and non-metals are on the right hand side. A zig-zag diagonal line divides metals and non-metals. Elements near the zig-zag line are called metalloids. Elements of the same group have the same number of valence electrons but different number of shells. Elements of the same period have different numbers of valence electrons but the same number of shells. Elements in the middle of the periodic table are called transition metals. Why are group 1 elements soft and have low melting and boil
  10. Q30 Why does the water in the deep sea appear blue in color?