most important questions, class 9th science

  1. Name the element which does not contain any neutron.
  2. Name two elements which have the same atomic number.
  3. An atom of an element is represented as 16/8 A. What is its atomic number and mass number? Also name the element.
  4. An atomof an element has 19 protons, 19 electrons and 20 neutrons.The atomic mass of the element is……….
  5. What is the maximum capacity of outermost shell of an atom?
  6. Name an element which has two valence electrons but is a noble gas.
  7. Which electrons determine the chemical properties of an element?
  8. An element has 8 electrons in its valence shell. What is its general name?
  9. Why isotopes have different mass numbers?
  10. Why do isotopes of an element have different physical properties ?An isotope of lead has a mass number 211 and atomic number 82 (211/82Pb).During radioactive disintegration,gets converted into an element whose mass number remains the same but atomic number increases by 1.Will the end product be an isobar or not ?
  11. What are isotopes?
  12. Write the value of charge on electron.
  13. Define mass number.
  14. Define valency.
  15. Explain the electrical nature of matter.
  16. What are cathode rays and positive rays?
  17. What is the nucleus of an atom?
  18. Define the term mass number giving an example.