Assertion :Assertion: In plant cells, during S-phase, DNA replication begins in the nucleus, and the centriole duplicates in the cytoplasm. Reason: If the initial amount of DNA is denoted as 2n at $G_1$, even after S-phase the amount of DNA remains the same i.e., 2n.

Q. Assertion: The compressibility factor for $H_2$​ and $He$ is $(1+\frac{Pb}{RT})$
Reason: The compressibility factor for $H_2$​ and $He$ can be derived from Van der Waal's equation.

Q.

Assertion (A) The enthalpy of reaction remains constant in the presence of a catalyst.

Reason (R) A catalyst participating in the reaction forms different activated complex and lowers down the activation energy but the difference in enrgy of reactant and product remains the same.

(a) Both assertion and reason are correct and the reason is correct explanation of assertion
(b) Both assertion and reason are correct, but reason does not explain assertion.
(c) Assertion is correct, but reason is incorrect
(d) Both assertion and reason are incorrect
(e) Assertion is incorrect but reason is correct.

Q. Assertion: The impurities such as ${\text{SiO}}_2$ present in iron ore is removed by ${\text{CaCO}}_3$.

Reason: $\text{CaO}$ formed by decomposition of ${\text{CaCO}}_3$ reacts with ${\text{SiO}}_2$ to form slag.

Q.

Assertion – The non-fusible impurities present in iron ore are removed by $CaC{O}_3$ .

Reason: $CaC{O}_3$ which decomposes into $CaO$ and $C{O}_2$. The $CaO$ formed reacts with $Si{O}_2$ to remove silica

Q. Assertion : Two electrons of helium atom are placed in only one shell but three electrons of lithium need two shells.
Reason: A shell can have maximum ${\text{2n}}^2$ electrons.