The number of moles present in 44 g of CO₂ is
A 0.5 mol
B 1.0 mol
C 2.0 mol
D 4.0 mol
Moles = mass / molar mass = 44 / 44 = 1 mol.
The number of atoms present in 23 g of sodium is
A 3.011×10233.011 \times 10^{23}3.011×1023
B 6.022×10236.022 \times 10^{23}6.022×1023
C 1.204×10241.204 \times 10^{24}1.204×1024
D 9.033×10239.033 \times 10^{23}9.033×1023
Atomic mass of Na = 23. So 23 g = 1 mol = Avogadro number of atoms.
Which of the following has the maximum number of atoms
A 16 g of O₂
B 14 g of N₂
C 18 g of H₂O
D 12 g of C
• 16 g O₂ = 0.5 mol molecules = 1 mol atoms
• 14 g N₂ = 0.5 mol molecules = 1 mol atoms
• 18 g H₂O = 1 mol molecules = 3 mol atoms
• 12 g C = 1 mol atoms
Maximum atoms → H₂O.
The limiting reagent is the substance
A Taken in excess
B Which reacts last
C Which produces maximum product
D Which is completely consumed first
The limiting reagent determines the maximum amount of product formed.
If empirical formula is CH and molecular mass is 78, the molecular formula is
A C₂H₂
B C₃H₃
C C₆H₆
D C₄H₄
Empirical mass of CH = 13. Factor = 78/13 = 6 → molecular formula = C₆H₆.
Which law explains that gases react in simple volume ratios
A Law of conservation of mass
B Law of constant proportions
C Law of multiple proportions
D Gay-Lussac’s law
It states that volumes of reacting gases bear simple whole-number ratios.
The maximum number of electrons with l = 2 is
A 2
B 6
C 10
D 14
l = 2 corresponds to d-subshell → 5 orbitals × 2 electrons = 10.
The number of subshells present in the 4th shell is
A 2
B 3
C 4
D 5
Number of subshells = n → for n = 4, subshells = s, p, d, f.
Which orbital has maximum penetration power
A 2p
B 3p
C 3s
D 3d
Penetration order: s > p > d > f. s-orbitals approach nucleus most closely.
Which statement is correct for spin quantum number
A It gives orbital shape
B It has values 0 and 1
C It has values +½ and −½
D It determines orbital orientation
Spin quantum number represents intrinsic spin of electron.
The electronic configuration of Cu (Z = 29) is
A [Ar] 4s² 3d⁹
B [Ar] 4s¹ 3d¹⁰
C [Ar] 4s² 3d¹⁰
D [Ar] 3d⁹ 4p²
Copper shows anomalous configuration due to extra stability of fully filled d-subshell.
Which element has the smallest atomic radius in period 2
A Li
B Be
C C
D F
Atomic radius decreases across a period; fluorine is smallest.
Ionization enthalpy decreases down a group because
A Atomic size decreases
B Shielding effect increases
C Nuclear charge decreases
D Electronegativity increases
Increased inner-shell electrons reduce nuclear attraction on valence electrons.
Which has the highest electron affinity
A O
B S
C Cl
D Ar
Chlorine releases maximum energy on gaining an electron.
Which element has the highest electronegativity
A Oxygen
B Nitrogen
C Fluorine
D Chlorine
Fluorine has highest electronegativity due to small size and high nuclear charge.
Metallic character increases
A Across a period
B With increasing atomic number
C Down a group
D With increasing electronegativity
Down the group, atoms lose electrons more easily.
Which oxide is strongly acidic
A Na₂O
B MgO
C Al₂O₃
D SO₂
Non-metal oxides are acidic; SO₂ forms sulphurous acid in water.
Which element belongs to p-block
A Na
B Ca
C Al
D Fe
Aluminium has valence electrons in p-subshell.
The element with configuration ns²np⁴ belongs to
A Group 14
B Group 15
C Group 16
D Group 17
Chalcogens have six valence electrons (ns²np⁴).
Which halogen has the largest atomic size
A F
B Cl
C Br
D I
Atomic size increases down the group.
Which species has zero unpaired electrons
A N
B O
C F
D Ne
Neon has completely filled orbitals → diamagnetic.
The correct order of increasing ionization enthalpy is
A Na < Mg < Al < Si
B Al < Mg < Na < Si
C Na < Al < Mg < Si
D Mg < Na < Al < Si
Ionization energy generally increases across period with known Al < Mg anomaly.
Which ion is smallest in size
A Na⁺
B Mg²⁺
C Al³⁺
D K⁺
Higher nuclear charge and greater positive charge reduce ionic radius.
Which compound shows maximum covalent character
A NaCl
B MgCl₂
C AlCl₃
D KCl
Fajan’s rule: small, highly charged cation → high covalent character.
The modern periodic table is based on
A Atomic mass
B Valency
C Atomic number
D Density
Moseley proved atomic number determines periodic properties.
Which element is a noble gas
A Nitrogen
B Neon
C Chlorine
D Sulfur
Noble gases have complete octet.
Which has the highest second ionization enthalpy
A Li
B Be
C Na
D Mg
Na⁺ has noble gas configuration; removing another electron is very difficult.
The total number of orbitals in n = 4 shell is
A 8
B 16
C 18
D 32
Total orbitals = n² = 4² = 16.
Which element has highest nuclear charge
A S
B Cl
C Ar
D K
Nuclear charge equals atomic number; K has highest Z among given.
Which statement is true
A Atomic size increases across a period
B Electronegativity decreases across a period
C Metallic character increases down a group
D Ionization energy decreases across a period
Down the group, electrons are lost more easily.
Which block contains transition metals
A s-block
B p-block
C d-block
D f-block
Transition metals have partially filled d-orbitals.
The element having maximum electron affinity in period 2 is
A C
B N
C O
D F
Fluorine readily gains an electron.
Which is a metalloid
A Na
B Mg
C Si
D Cl
Silicon shows intermediate metallic and non-metallic properties.
Which subshell is filled last according to Aufbau principle
A 4s
B 3d
C 4p
D 5s
4s is filled before 3d; 3d fills later.
Which atom has maximum unpaired electrons
A C
B N
C O
D F
Nitrogen (2p³) has three unpaired electrons.
Which element has lowest electronegativity
A Li
B Na
C K
D Cs
Electronegativity decreases down the group.
Which pair shows diagonal relationship
A Li – Mg
B Be – B
C C – N
D O – F
Diagonal relationship occurs between 2nd and 3rd period elements.
Which has highest charge density
A Na⁺
B Mg²⁺
C Al³⁺
D Ca²⁺
High charge and small size → high charge density.
Which element is chemically inert
A Nitrogen
B Oxygen
C Neon
D Chlorine
Noble gases do not normally react.
Which element has configuration ending with p⁵
A O
B N
C Cl
D Ar
Halogens have ns²np⁵ configuration.
The most basic oxide is
A MgO
B Al₂O₃
C Na₂O
D SiO₂
Alkali metal oxides are strongly basic.
The number of electrons in 2p subshell is maximum equal to
A 2
B 4
C 6
D 8
p-subshell has three orbitals → 6 electrons.
Which has the greatest reducing power
A Li
B Na
C K
D Cs
Reducing power increases down the alkali metal group.
Which statement is incorrect
A Atomic number increases across period
B Atomic size decreases across period
C Ionization energy decreases across period
D Electronegativity increases across period
Ionization energy actually increases across a period.
Which element has filled valence shell
A Na
B Mg
C Ne
D Cl
Noble gases have completely filled valence shells.
Which element belongs to group 17
A O
B N
C Cl
D Ar
Chlorine is a halogen (group 17).
The atomic number of an element is determined by
A Number of neutrons
B Number of protons
C Number of electrons
D Mass number
Atomic number equals number of protons.
Which factor does not affect ionization energy
A Nuclear charge
B Atomic size
C Shielding effect
D Temperature
Ionization energy depends on electronic factors, not temperature.
Which element has configuration ns¹
A Alkali metals
B Alkaline earth metals
C Halogens
D Noble gases
Alkali metals have one valence electron.
Which periodic property shows irregular trend
A Atomic radius
B Ionization energy
C Metallic character
D Atomic number
Due to subshell stability (half-filled, filled), ionization energy shows exceptions.