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#1
By Ahmed Akber
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Hard
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Fact Checked
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06 Apr 2026
Which condition must be met for a chemical reaction to be spontaneous at all temperatures?
💡 Explanation:According to the Gibbs free energy equation (G = H - TS), a reaction is spontaneous (G < 0) at all temperatures only when it is exothermic (H < 0) and leads to an increase in disorder (S > 0).
#2
By Rabia Anum
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Medium
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Fact Checked
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04 Mar 2026
How does a catalyst primarily increase the rate of a chemical reaction?
💡 Explanation:A catalyst functions by providing an alternative reaction pathway with a lower activation energy. This allows a greater fraction of collisions between molecules to result in a reaction without the catalyst being consumed.
#3
By Rabia Anum
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Medium
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Fact Checked
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22 Feb 2026
What element possesses the highest electronegativity on the Pauling scale?
💡 Explanation:Fluorine is the most electronegative element with a value of 3.98, meaning it has the strongest tendency to attract shared electrons in a chemical bond.
#4
By Rabia Anum
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Medium
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Fact Checked
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13 Feb 2026
Which subatomic particle primarily determines an element’s chemical properties?
💡 Explanation:The chemical properties of an element, such as its reactivity and ability to form bonds, are determined by the configuration of its electrons, particularly the valence electrons in the outermost shell.
#5
By Kalsoom Tahir
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Medium
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Fact Checked
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23 Jan 2026
If a fixed amount of ideal gas has its absolute temperature doubled and volume halved, what change occurs in its pressure?
💡 Explanation:This problem is solved using the Combined Gas Law, P1V1/T1 = P2V2/T2, for a fixed amount of gas (n is constant). If the absolute temperature (T) is doubled (T2 = 2T1) and the volume (V) is halved (V2 = 0.5V1), the final pressure (P2) is calculated as P2 = P1 <strong> (V1/V2) </strong> (T2/T1) = P1 <strong> (V1 / 0.5V1) </strong> (2T1 / T1) = P1 <strong> 2 </strong> 2 = 4P1. The pressure quadruples.
#6
By Kalsoom Tahir
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Easy
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Fact Checked
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19 Jan 2026
What subatomic particle’s number uniquely defines an element and is its atomic number?
💡 Explanation:The atomic number (Z) of an element is defined by the number of protons in the nucleus. Changing the number of protons changes the element itself. The number of neutrons can change to form an isotope, and the number of electrons can change to form an ion, neither of which changes the fundamental identity (element) of the atom.
#7
By Rabia Anum
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Hard
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Fact Checked
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15 Jan 2026
Which factor allows polymerization, a process with negative entropy change ((Delta S < 0)), to be thermodynamically spontaneous?
💡 Explanation:The criterion for a spontaneous process is a negative change in Gibbs free energy ((Delta G < 0)), according to the equation (Delta G = Delta H - TDelta S). Polymerization is the linking of small monomers into a large polymer chain, which decreases the total number of free molecules, resulting in a negative entropy change ((Delta S < 0)). For the reaction to still be spontaneous ((Delta G < 0)), the enthalpy change ((Delta H)) must be highly negative (exothermic) to overcome the positive term of (-TDelta S), especially at lower temperatures where the spontaneity is often observed.
#8
By Ahmed Akber
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Hard
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Fact Checked
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01 Jan 2026
Which periodic group element acts as a donor impurity to dope pure silicon?
💡 Explanation:Silicon is a Group 14 element (4 valence electrons). A donor impurity, which creates an n-type semiconductor, must be an element with five valence electrons, found in Group 15 (e.g., Phosphorus or Arsenic). The fifth valence electron is not required for bonding and is 'donated' to the conduction band.
#9
By Kalsoom Tahir
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Medium
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Fact Checked
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25 Dec 2025
How many grams of $text{H}_2text{O}$ are produced by the complete combustion of 16g of $text{CH}_4$?
💡 Explanation:The balanced chemical equation for the complete combustion of methane is $text{CH}_4 + 2text{O}_2 rightarrow text{CO}_2 + 2text{H}_2text{O}$. The molar mass of methane ($text{CH}_4$) is approximately $16 text{ g/mol}$ and the molar mass of water ($text{H}_2text{O}$) is $18 text{ g/mol}$.
Step 1: Convert mass of $text{CH}_4$ to moles.
$text{Moles of } text{CH}_4 = text{Mass} / text{Molar Mass} = 16text{g} / 16 text{ g/mol} = 1 text{ mole}$.
Step 2: Use stoichiometry to find moles of $text{H}_2text{O}$.
The equation shows a $1:2$ mole ratio between $text{CH}_4$ and $text{H}_2text{O}$.
$text{Moles of } text{H}_2text{O} text{ produced} = 1 text{ mole } text{CH}_4 times (2 text{ moles } text{H}_2text{O} / 1 text{ mole } text{CH}_4) = 2 text{ moles}$.
Step 3: Convert moles of $text{H}_2text{O}$ to mass.
$text{Mass of } text{H}_2text{O} = text{Moles} times text{Molar Mass} = 2 text{ moles} times 18 text{ g/mol} = 36 text{ grams}$.
#10
By Ahmed Akber
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Medium
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Fact Checked
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19 Dec 2025
For a gaseous reaction where $4$ moles of reactants yield $2$ moles of products, how does increased pressure shift equilibrium?
💡 Explanation:According to Le Chatelier's principle, increasing the pressure on a gaseous system at equilibrium will cause the system to shift towards the side with the fewer total moles of gas to counteract the stress. Since 4 moles (reactants) yield 2 moles (products), the shift favors the product side.
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