Radioactivity another name for radioactive decay. Radioactivity refers to particles emitted from nuclei as a result of nuclear instability.
Density of the gas is 3.05 × 10⁻³ g / cm³.
<u>Explanation:</u>
Volume of the cylinder = π r² h
where r is the radius and h is the height of the height or the length of the glass tube.
Here r = 4 cm and h = 27.4 cm
Volume of the cylinder = 3.14 × 4 × 4 × 27.4 = 1376.6 cm³
We have to find the mass of the gas by subtracting the mass of the tube filled with the substance from the mass of the empty tube.
Mass of the substance = 258.5 - 254.3 = 4.2 g
We have to find the density using the formula as,

Plugin the values as,
= 3.05 × 10⁻³ g / cm³
So the Density of the gas is 3.05 × 10⁻³ g / cm³.
Answer : Option A) HF.
Explanation : Assuming the complete question as per the attachment.
H-F bonds are formed because of hydrogen bonding between H atom and F atom and is considered to be strongest amongst the rest other options given.
As given in the table it is clear that the molar mass of HF molecule is the lowest. It shows that, when dispersion increases in the molecule molecular weight also increases.
Answer: Acceleration and velocity
Explanation:
Newton's second law says that when a constant force acts on a massive body, it causes it to accelerate, i.e., to change its velocity, at a constant rate. In the simplest case, a force applied to an object at rest causes it to accelerate in the direction of the force.