Protium is the most abundant isotope of hydrogen. It contains only one proton and no neutrons are present. It is basically a hydrogen atom.

Nitration of benzene is an electrophilic substitution reaction, in which $NO_2^+$ (nitronium ion) electrophile attacks the benzene ring.

America dropped the atom bomb on Hiroshima city of Japan for the first time on August 6, 1945.

The properties of an element are determined by their atomic number, because the atomic number determines the configuration of electrons, which are responsible for chemical behavior.

Carbon-14 (a radioactive isotope) is used in determining the age of carbon-containing objects. This method of age determination is called Carbon Dating.

Correct match: (A) Hydrogen bomb - (2) Fusion, (B) Atomic bomb - (1) Fission, (C) Binding energy - (4) Mass defect, (D) Nuclear reactor - (3) Critical mass. Code (3) is correct.

A molecule is the smallest particle of a compound that possesses all the properties of that compound.

India's first nuclear reactor is 'Apsara', which became operational in 1956.

Dynamite is an explosive. Trinitroglycerin (T.N.G.) is used in its construction. It was discovered by Alfred Nobel in 1863 AD. It is a colorless liquid.

TNT, i.e., Trinitrotoluene is the world's most widely used solid military explosive. It is a yellow solid organic compound that turns from a solid state into rapidly expanding gases.

The atomic nucleus was discovered by Rutherford in 1911. Protons and neutrons are found in the nucleus.

Radio carbon-dating is used to determine the age of fossils. Carbon-14 found in fossils undergoes decay.

Isotopes are atoms of the same element that have the same atomic number but different mass numbers (atomic weight). Isotopes have the same number of protons.

Two elements which have different atomic numbers (number of electrons) but the same mass number are called Isobars. This is because the number of nucleons (protons + neutrons) in their nucleus is the same.

Elements that have the same number of protons or atomic number and different number of neutrons are called isotopes. E.g. $_{20}Ca^{40}, _{20}Ca^{41}$.

'Canal Ray' - E. Goldstein discovered new radiation in 1886 which was named Canal Ray. These were positively charged radiations and their charge was equal but opposite to that of an electron. These have been named protons.

The half-life of a radioactive material is 10 days. This means that after 10 days half the amount remains, and after 20 days (two half-lives) half of the remaining half (i.e., 1/4) remains, which means 3/4 of the part would have decayed.

The size of alkali metals is the largest in any particular period of the periodic table. As the atomic number increases, the size of the atom increases. The size of alkali metals is smaller than their parent atoms. The atomic and ionic radii of alkali metals increase as we move from top to bottom in a group, meaning their size increases from Li to Cs.

5 molecules of water are attached to the crystals of Copper Sulfate Pentahydrate ($CuSO_4 \cdot 5H_2O$).

According to Dalton's atomic theory, all matter, whether element, compound, or mixture, is made of small particles called atoms. (i) All matter is made of atoms, which take part in chemical reactions. (ii) Atoms are indivisible smallest particles which are neither created nor destroyed in a chemical reaction. (iii) All atoms of a given element have identical mass and chemical properties. (iv) Atoms of different elements have different masses and chemical properties. (v) Atoms of different elements combine in small whole number ratios to form compounds. (vi) The relative number and kind of atoms are constant in a given compound. Thus, statement 3 is incorrect.