Following questions consist of two statements – Assertion (A) and Reason (R). Answer these questions selecting the appropriate option given below:
(a) Both A and R are true and R is the correct explanation of A.
(b) Both A and R are true but R is not the correct explanation of A.
(c) A is true but R is false.
(d) A is false but R is true.
Q.1. Assertion (A) : Mendeléev concentrated on the compounds formed by elements with oxygen and hydrogen in his periodic table.
Reason (R) : Hydrogen and oxygen are very reactive and form compounds with most elements.
Answer
(a)Q.2. Assertion (A) : In Mendeléev Periodic Table, cobalt was placed before nickel.
Reason (R): The atomic mass of cobalt is less than nickel.
Answer
(c)Q.3. Assertion (A) : According to Mendeléev, the properties of elements are a periodic function of their atomic masses.
Reason (R) : Atomic number is equal to the number of protons.
Answer
(b)Q.4. Assertion (A) : Noble gases have zero valency.
Reason (R) : Noble gases have stable electronic configuration.
Answer
(a)Q.5. Assertion (A) : Elements in the same vertical column have similar properties.
Reason (R) : Elements have periodic dependence upon the atomic number.
Answer
(b)Q.6. Assertion (A) : Silicon is a metalloid.
Reason (R) : Silicon shows only properties of non-metals.
Answer
(c)Q.7. Assertion (A) : Fluorine has greater atomic radius than nitrogen.
Reason (R): Atomic radius decreases along a period.
Answer
(d)Q.8. Assertion (A): Li, Na, K form Döbereiner’s triads.
Reason (R) : Atomic mass of Na is roughly the average of atomic masses of Li and K.
Answer
(a)Q.9. Assertion (A) : Magnesium belongs to 3rd period of modern periodic table.
Reason (R) : The valence electrons of magnesium is 2.
Answer
(b)Q.10. Assertion (A) : Isotopes are placed together in the modern periodic table.
Reason (R) : Isotopes have same atomic number.