Ans 1) Atomic mass.
Reason : Mendeleev organized elements in his periodic table in order of increasing atomic mass.
Mendeleev believed that physical & chemical props of any elements were related to their atomic mass in a periodic way, then he arranged them into groups of elements with same props fell into vertical columns in his table in increasing atomic mass of the elements.
Ans 2) Highest melting point.
Reason : You are given the melting points of three unknown substances & are asked to predict which one is an ionic compound. You would select the compound with the highest melting point.
As ionic bonds require high amount of energy to break the ionic bonding btwn d atoms because these bonds are much stronger so usually they have high melting
Ans 3) Configuration.
Reason : 2 factors that determine whether a molecule is polar are d types of atoms in d molecule & d configuration of d molecule.
Polar molecules must contain polar bonds in their structure & configuration due to d difference in electronegativity btwn d bonded atoms.
Ans 4) A) The ratio of their masses is always the same.
Reason : John Dalton's observation when d elements combine in compound d ratio of their masses always d same
Dalton's theory proved that all d matter were composed of atoms, & when they combine with identical or different elements d ratio of their masses was always found to be same.
Ans 5) A) Of earth, air, fire, & water.
Reason : Democritus thought matter was made of tiny particles of earth, air, fire & water. He was d first to propose that it consists of atoms which are made up from earth, air, water & fire.
Ans 6) D) There is a dense, positively charged mass in d center of an atom.
Reason : Rutherford's gold foil experiment provided evidence for a dense, positively charged mass in d center of atom.
He made assumptions that atoms mainly contain empty space with (-) vely charged electrons surrounding around d nucleus in defined orbits, also he concluded that there is a dense, positively charged mass in d center of atomic nucleus.
Ans 7) A) Protons, neutrons, & electrons all have about d same mass.
Reason : D subatomic particles consists of protons, neutrons & electrons.
Atoms consists of protons which are positively charged, electrons are negatively charged species which revolves around d nucleus in defined circular orbits & neutrons are neutral species.
Ans 8) C) They are isotopes of oxygen
Reason : Oxygen-17 & Oxygen-18 are isotopes of oxygen. An isotope are each of 2 or more forms of d same element which contains equal numbers of protons but different numbers of neutrons in their atomic nuclei. They are found to differ in relative atomic mass but not in chemical props.
Ans 9) B) Electrons travel around d nucleus in fixed energy levels with energies that vary from level to level.
Reason : Bohr's atomic model for arrangement of electrons accurately stated that electrons travel around d nucleus in fixed energy levels with energies that varies from level to level.
Bohr found that in atoms electrons are found to follow defined circular path to revolve around d nucleus. It has many levels around d nucleus, which had different energies for different levels.
Ans 10) A) D most likely locations of electrons in atoms.
Reason : D electron cloud model described d most likely locations of electrons in atom.
Electron cloud is used to describe d probability of finding electrons when they revolve around d nucleus of an atom. D electron cloud model was observed to be different than d older Bohr atomic model.
Ans 11) C) The atom in an excited state has more energy & is less stable than d atom in d ground state.
Reason : The difference btwn d atom in d ground state & atom in excited state is atom in an excited state has more energy & is less stable than d atom in d ground state.
Atoms that were excited had high energy but their stability was found to be low, it stayed for less time in this state. When it came back to ground state it had lower energy but higher stability than that of excited state.
Ans 12) C) d discovery of elements with predicted props
Reason : D usefulness of Mendeleev's periodic table was confirmed by d discovery of elements with d predicted props.
Mendeleev assumed that elements have physical & chemical props related to their atomic masses, so he arranged d elements according to d at. masses & d atoms with similar props fell into same groups which was later on discovered to be true in nature.
Ans 13) A) one or seven valence electrons.
Reason : Atoms of most reactive elements tend to have one or seven valence electrons.
It seen that highly reactive elements have valence shell with 1 electron were highly reactive cations, whereas d elements which had 7 electrons in valence shell were highly reactive anions. This was because to donating 1 electron was easy, but for seven electrons it was easy to gain 1 electron & achieve d octet state.
