Lavoisier is known for the law of conservation of mass, naming oxygen/hydrogen, and establishing chemistry as a quantitative science. Dalton proposed atomic theory; Mendeleev periodic table.
Explanation:
Atomic radius decreases across a period due to increasing nuclear charge. Sodium (Na) is the first element in period 3, thus it has the largest atomic radius. Argon (noble gas) has the smallest (though noble gas radii are van der Waals and larger than covalent, but still trend is decreasing). For metals, Na > Mg > Al; non-metals further smaller.
Assertion (A): Aluminum is highly reactive but is used for making cooking utensils. Reason (R): Aluminum forms a protective layer of aluminum oxide on its surface.
A.Both A and R are true and R is the correct explanation of A.
B.A is true but R is false.
C.A is false but R is true.
D.Both A and R are true but R is NOT the correct explanation of A.
Explanation:
Aluminum is a highly reactive metal, yet it is widely used for cookware. This is because it rapidly reacts with atmospheric oxygen to form a thin, tough, and invisible layer of aluminum oxide (Al2O3) on its surface. This passivation layer prevents further corrosion and reaction with food.
Explanation:
Mendeleev arranged elements in order of increasing atomic mass, grouping those with similar properties. He left gaps for undiscovered elements. Modern table uses atomic number.
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