1. (c) The region in space where an electron is likely to be found is called an orbital. There are different kinds of orbitals with different sizes and shapes. The orbital at the lowest energy level is defined as a 1s orbital. It is a sphere with its center at the nucleus of the atom. The next higher energy level is called a 2s orbital. It is larger than a 1s orbital. Since it has a higher energy level, it has lower stability compared to a 1s orbital. This is because the average distance between the nucleus and electrons in a 2s orbital is greater than in a 1s orbital. The next three orbitals are of equal energy, known as 2p orbitals. They are dumbbell-shaped. They are further differentiated by the names 2px, 2py, and 2pz, where the x, y, and z refer to the corresponding axes.

2. (d) In the covalent bond, two atoms are joined by sharing electrons. Both nuclei are held by the same electron cloud. However, in most cases the two nuclei do not share the electrons equally. This happens when one atom has more electron withdrawing power than the other atom. At this time the electron cloud is denser on one atom. This result in one end of the bond being relatively negative and the other end being relatively positive. Such a bond is said to be a polar bond or to possess polarity. The bond possesses polarity when joins atoms have different tendency to attract electrons. This property of the atom is called electronegativity. Out of the given choices, fluorine (F) possess the highest electronegativity. F > O > Cl, N > Br > C, H

3. (c) The molecular formula for methyl chloride is CH3Cl. The mass of a chlorine atom in methyl chloride is 35.5 gm/mole. The molecular weight of methyl chloride is 50.5 gm/mole (1C = 12, 3H = 3 and 1Cl = 35.5). Therefore, the % mass of chlorine in methyl chloride will be 35.5/50.5 = 70%

4. (b) Isotopes are defined as forms of the same chemical element that differ only by the number of neutrons in their nucleus. Most elements have more than one naturally occurring isotope. The atomic number "Z" is the same in such elements, however their atomic mass "A" is different due to differ numbers of neutrons in the nucleus of the atom.

5. (a) The alkali metals, found in group 1 of the periodic table (formerly known as group IA), are very reactive metals that do not occur freely in nature. These metals have only one electron in their outer shell. Therefore, they are ready to lose that one electron in ionic bonding with other elements. As with all metals, the alkali metals are malleable, ductile, and are good conductors of heat and electricity. The alkali metals are softer than most other metals. Cesium and francium are the most reactive elements in this group. Alkali metals can explode if they are exposed to water. The Alkali Metals are: lithium (Li), Sodium (Na), Potassium (K), Rubidium (Rb), Cesium (Cs), Francium (Fr).