Cardiac muscles contract:

The rate of disintegration of a fixed quantity of a radioactive element can be increased by

For all values of $\theta$,the values of $3-\cos \theta+\cos \left(\theta+\frac{\pi}{3}\right)$ lie in the interval :

$A$ nucleus ${}_{n}^{m}X$ emits one $\alpha$ particle and two ${\beta^-}$ particles. The resulting nucleus is

$A$ radioactive nucleus undergoes a series of decays according to the scheme:
$A \xrightarrow{\alpha} A_1 \xrightarrow{\beta} A_2 \xrightarrow{\alpha} A_3 \xrightarrow{\gamma} A_4$
If the mass number and atomic number of $A$ are $180$ and $72$ respectively,what are these numbers for $A_4$?

$A$ gaseous mixture contains $50\%$ helium and $50\%$ methane by volume. What is the percentage of methane by weight in the mixture?