Science Assertion - Reasoning [Che-1 M]

1. Both the Assertion and the Reason are correct and the Reason is the correct explanation of the Assertion.

Explanation:

Atom is electrically neutral as it has same number of electrons and protons. When electrons are removed, a positively charged ion called cation is formed and when electrons are added, negatively charged ion called anion is formed.

2. The Assertion and the Reason are correct but the Reason is not the correct explanation of the Assertion.

Explanation:

A neutral atom has the same number of protons and electrons. The proton number is the atomic number of the element, while the electron number is the atomic number minus the charge. A negatively-charged ion or anion has more electrons than protons.

Its nucleus also contains two neutrons. Since 2 + 2 = 4, we know that the mass number of the helium atom is 4. Finally, the helium atom also contains two electrons, since the number of electrons must equal the number of protons. 

4. If Assertion is false but Reason is true.

Explanation:

Boron has a valency of 3 and carbon has a valency of four; since the outermost shell has 3 and 4 electrons respectively. Since fluorine has 7 electrons in the outermost orbit it loses one electron to attain the octet configuration. So the valency of fluorine is 1.

The number of electrons present in the outermost shell of an atom are known as the valence electrons.

3. If Assertion is true but Reason is false.

Explanation:

Bohr's orbits are called as stationary states because as we know that if an object moves in circular path it will lose energy but, according to bohr electrons which is moving in the circular path does not lose energy. If electrons lose energy they will fall into nucleus and get burnt.

1. If both Assertion and Reason are true and Reason is the correct explanation of Assertion.

Explanation:

Electrons in atoms orbit the nucleus. The electrons can only orbit stably, without radiating, in certain orbits (called by Bohr the “stationary orbits”) at a certain discrete set of distances from the nucleus. These orbits are associated with definite energies and are also called energy shells or energy levels.

These orbits are stable and called "stationary" orbits. Electrons in these orbits do not radiate their energy away. Each orbit is associated with a definite value of the energy and the angular momentum.