In Millikan's experiment,static electric charge on the oil drops has been obtained by shining $X$-rays. If the static electric charge on the oil drop is $-1.282 \times 10^{-18} \ C,$ calculate the number of electrons present on it.

The ratio of specific charge of a proton and an $\alpha$-particle is

The nucleus of the atom consists of

The relationship between the radius of the nucleus $(R)$ and the mass number $(A)$ is given by .......

Positronium is the name given to an atom-like combination formed between

Fill in the blanks given below:
$(i)$ The circular path around the nucleus in which electrons revolve at high speed is called ......... .
$(ii)$ Electrons and the nucleus are held together by ......... force.
$(iii)$ The number of $P^{+}$ in the nucleus and the sum of the number of $P^{+}$ and $n^{\circ}$ in the nucleus are represented by the symbols ...... and ......... respectively.
$(iv)$ The sum of the number of $P^{+}$ and $n^{\circ}$ in the nucleus is represented by the term ...... and the symbol .... respectively.