The number of significant figures in 0.004560 is
A 3
B 4
C 5
D 6
Leading zeros are not significant. Significant figures are 4, 5, 6, and trailing zero after decimal → total 4.
Which law states that mass is neither created nor destroyed in a chemical reaction
A Law of multiple proportions
B Law of constant proportions
C Law of conservation of mass
D Avogadro’s law
Proposed by Lavoisier, it states that total mass of reactants equals total mass of products.
1 mole of any substance contains
A 6.022×10226.022 \times 10^{22}6.022×1022 particles
B 6.022×10236.022 \times 10^{23}6.022×1023 particles
C 3.011×10233.011 \times 10^{23}3.011×1023 particles
D 1.204×10241.204 \times 10^{24}1.204×1024 particles
Avogadro’s number defines one mole of any substance.
Which of the following is not an isotone
A 614C^{14}_6C614C and 715N^{15}_7N715N
B 816O^{16}_8O816O and 917F^{17}_9F917F
C 612C^{12}_6C612C and 613C^{13}_6C613C
D 818O^{18}_8O818O and 919F^{19}_9F919F
Isotones have same neutrons. Option C are isotopes (same Z, different A).
The maximum number of electrons with n = 4 and l = 1 is
A 2
B 6
C 10
D 14
l=1 means p-subshell → 3 orbitals × 2 electrons each = 6.
Which quantum number determines orientation of orbital
A Principal quantum number
B Azimuthal quantum number
C Magnetic quantum number
D Spin quantum number
Magnetic quantum number (m) specifies spatial orientation of orbital.
Which orbital has zero probability of finding electron at nucleus
A 1s
B 2s
C 2p
D 3s
p-orbitals have nodal plane passing through nucleus; probability at nucleus is zero.
Total number of orbitals in third shell is
A 3
B 5
C 9
D 18
Total orbitals in shell = n² = 3² = 9.
Which has completely filled subshell
A Nitrogen
B Oxygen
C Neon
D Fluorine
Neon has configuration 1s²2s²2p⁶ → all subshells filled.
Which element has half-filled p-subshell
A Carbon
B Nitrogen
C Oxygen
D Fluorine
Nitrogen has 2p³ configuration → half-filled p-subshell.
The number of electrons in p-orbitals of sulfur is
A 2
B 3
C 4
D 6
Sulfur (Z=16): [Ne]3s²3p⁴ → 4 electrons in p-subshell.
Which pair is isoelectronic
A Na⁺ and Mg²⁺
B O²⁻ and F⁻
C N³⁻ and O²⁻
D All of these
Each pair has equal number of electrons → isoelectronic species.
Which subshell penetrates closest to nucleus
A s
B p
C d
D f
s-orbitals have maximum penetration due to spherical symmetry.
Shielding effect is maximum for
A s electrons
B p electrons
C d electrons
D f electrons
s-electrons shield nuclear charge most effectively.
Which has smallest atomic radius
A Li
B Be
C B
D C
Atomic radius decreases across a period due to increasing effective nuclear charge.
Which element has highest electron affinity in second period
A Oxygen
B Nitrogen
C Fluorine
D Neon
Fluorine strongly attracts electrons to complete octet.
Which noble gas has highest ionization enthalpy
A He
B Ne
C Ar
D Kr
Helium has smallest size and highest effective nuclear charge.
Which element shows maximum metallic character
A Sodium
B Magnesium
C Aluminium
D Silicon
Metallic character decreases across a period; Na is leftmost.
Which oxide is amphoteric
A Na₂O
B MgO
C Al₂O₃
D SiO₂
Aluminium oxide reacts with both acids and bases.
Which element has highest atomic volume
A Na
B Mg
C Al
D Si
Alkali metals have largest atomic volumes in their periods.
The element with configuration [Ar]3d⁵4s¹ is
A Chromium
B Manganese
C Iron
D Vanadium
Chromium shows anomalous configuration due to half-filled d-subshell stability.
Which pair shows diagonal relationship
A Be and Mg
B Li and Mg
C B and C
D Al and Si
Diagonal relationship exists between second and third period elements.
Which has maximum ionization enthalpy
A Alkali metals
B Halogens
C Noble gases
D Alkaline earth metals
Noble gases have stable electronic configuration.
Which period contains maximum number of elements
A First
B Second
C Third
D Sixth
Sixth period contains 32 elements including lanthanides.
Which block element has valence electrons in p-subshell
A s-block
B p-block
C d-block
D f-block
p-block elements have valence electrons in p-orbitals.
Which element has maximum electronegativity in period 3
A Sulfur
B Chlorine
C Phosphorus
D Silicon
Electronegativity increases across period; chlorine is highest.
Which species is paramagnetic
A N₂
B O₂
C F₂
D Ne₂
O₂ has two unpaired electrons in antibonding orbitals.
Which orbital has highest energy in multi-electron atoms
A 2s
B 2p
C 3s
D 3p
Energy increases with (n + l); highest value corresponds to highest energy.
The value of l for f-subshell is
A 1
B 2
C 3
D 4
f-subshell corresponds to l = 3.
Which element has greatest tendency to lose electron
A Fluorine
B Oxygen
C Sodium
D Magnesium
Alkali metals easily lose valence electron due to low ionization energy.
Which has zero electron affinity
A Helium
B Neon
C Argon
D All of these
Noble gases have stable configuration and do not gain electrons.
Which species has maximum number of unpaired electrons
A N
B O
C F
D Ne
Nitrogen has 3 unpaired electrons in p-orbitals.
Which orbital does not exist
A 1p
B 2s
C 3d
D 4f
For n=1, only l=0 is allowed → only 1s exists.
Which quantum number has fractional values
A n
B l
C m
D s
Spin quantum number has values +½ or −½.
Which element forms most stable anion
A Oxygen
B Nitrogen
C Fluorine
D Chlorine
Chloride ion is larger and more stable than fluoride.
The maximum oxidation state of p-block elements is equal to
A Group number
B Period number
C Atomic number
D Valency only
Maximum oxidation state corresponds to total valence electrons.
Which element has smallest ionic radius
A Na⁺
B Mg²⁺
C Al³⁺
D Si⁴⁺
Higher nuclear charge and higher positive charge reduce ionic size.
Which shows highest covalent character
A NaCl
B MgCl₂
C AlCl₃
D KCl
According to Fajan’s rule, small highly charged cation increases covalent character.
Which factor does not affect periodicity
A Atomic number
B Shielding effect
C Nuclear charge
D Temperature
Periodic properties depend on electronic structure, not temperature.
Which is the correct trend of electronegativity
A Increases down the group
B Decreases across period
C Increases across period
D Constant in group
Electronegativity increases from left to right.
The modern periodic law is based on
A Atomic mass
B Atomic number
C Valency
D Density
Moseley established periodic law based on atomic number.
Which has maximum nuclear charge
A Na
B Mg
C Al
D Cl
Nuclear charge increases with atomic number.
Which element has lowest ionization enthalpy in period 3
A Na
B Mg
C Al
D Si
Alkali metals have lowest ionization energy.
Which group elements have ns²np⁵ configuration
A Group 13
B Group 14
C Group 16
D Group 17
Halogens have 7 valence electrons.
Which subshell is filled last in Aufbau order
A 4s
B 3d
C 4p
D 5s
4s fills before 3d, but 3d is filled later.
Which is most stable electronic configuration
A Half-filled subshell
B Completely filled subshell
C Single electron
D Empty subshell
Fully filled subshells have minimum energy.
Which element has configuration ending with 3p⁶
A Argon
B Chlorine
C Sulfur
D Phosphorus
Argon completes 3p subshell.
Which element has largest size among halogens
A F
B Cl
C Br
D I
Atomic size increases down the group.
Which statement is correct
A Ionization energy increases down the group
B Electron affinity decreases across period
C Metallic character increases down the group
D Atomic size decreases down the group
Atoms lose electrons more easily down a group.
Which element is chemically inert
A Nitrogen
B Oxygen
C Neon
D Chlorine
Noble gases have stable octet configuration.