A) 2 free protons
B) helium atoms
C) singly ionised helium atoms
D) doubly ionised helium atoms
Correct Answer: D
Solution :
Alpha particle is a positive particle. An alpha particle has \[3.2\times {{10}^{-19}}C\] charge twice the negative charge of an electron. The mass of a \[\alpha \]-particle is \[6.645\times {{10}^{-27}}\,kg\] which is equal to mass of helium nucleus. When two electrons are emitted by a helium atom, a nucleus of helium remains which has charge equal to that of two electrons. Actually alpha \[(\alpha )\] panicle is a nucleus of helium. Hence, it is also called as doubly-ionised helium atom.
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