\(\alpha\)-particle is made up of

Outermost shell of an atom cannot accommodate more electrons than

The nucleus of an atom is approximately

Chlorine, argon, potassium, calcium have no. electron as 17, 18, 19, 20 respectively.Their nucleus contains 18, 22,20,20 neutrons respectively.The pair of isobars are

Which one of the following is a correct electronic configuration of sodium?

How is the flow of current in a cathode ray experiment explained knowing that gases are bad conductors of electricity?

Give the mass and charge of an electron

What observation led to the conclusion that the nature of the anode rays depend upon the gas in the cathode rays tube?

What are cathode rays and positive rays?

What is a neutron? What are its characteristics?

Rutherford's \(\alpha\)-particle scattering experiment give the experimental evidence for deriving the conclusion that
(i) Most of the space inside the atom is empty
(ii) The nucleus of an atom is positively charged.

How do you define valency of an atom?

Define the term "Half-life".

The half-life period of Actinium is 15 seconds.Starting with 0.1g of Actinium, how much would be left at the end of one minute?

Give reasons for the following:
(a) Isotopes of an element are chemically similar
(b) An atom is electrically neutral
(c) Noble gases show least reactivity
(d) Nucleus of an atom is heavy and positively charged.
(e) Ions are more stable atoms.

Summarise the rules for writing of distribution of electrons in various shells for the first eighteen elements.

Explain with examples
(i) Atomic number,
(ii) Mass number,
(iii) Isotopes and
(iv) Isobars. Give any two uses of isotopes.

What are important properties of cathode rays?

Give four characteristics of cathode rays