Which part of the body secretes the hormone secretin?

$A$ series combination of resistor $(R)$ and capacitor $(C)$ is connected to an $A$.$C$. source of angular frequency $\omega$. Keeping the voltage same,if the frequency is changed to $\omega / 3$,the current becomes half of the original current. Then the ratio of the capacitive reactance and resistance at the former frequency is

Two satellites of earth $S_1$ and $S_2$ are moving in the same orbit. The mass of $S_1$ is four times the mass of $S_2$. Which one of the following statements is true?

Assertion $A$: Barium is not required in the normal biological processes of the human body.
Reason $R$: Barium does not exhibit more than one oxidation state.

Which one of the following is not a correct statement?

Which gas is released when $Na_2CO_3$ is heated?