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important questions for class 9th science
- Name the element which does not contain any neutron.
- Name two elements which have the same atomic number.
- An atom of an element is represented as 16/8 A. What is its atomic number and mass number? Also name the element.
- An atomof an element has 19 protons, 19 electrons and 20 neutrons.The atomic mass of the element is……….
- What is the maximum capacity of outermost shell of an atom?
- Name an element which has two valence electrons but is a noble gas.
- Which electrons determine the chemical properties of an element?
- An element has 8 electrons in its valence shell. What is its general name?
- Why isotopes have different mass numbers?
- 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 ?
- What are isotopes?
- Write the value of charge on electron.
- Define mass number.
- Define valency.
- Explain the electrical nature of matter.
- What are cathode rays and positive rays?
- What is the nucleus of an atom?
- Define the term mass number giving an example.