Explanation

An exothermic reaction releases heat to the surroundings.

Examples include combustion and neutralization reactions.

An endothermic reaction absorbs heat from the surroundings.

Examples include photosynthesis and melting of ice.

Explanation

The ion that is not a molecular ion is b) NH4+. 

A molecular ion is formed when a molecule gains or loses an electron, but NH4+ (ammonium ion)

It is not formed by removing an electron from a neutral molecule; it is formed by adding a proton (H+) to ammonia (NH3).

He+ (helium ion) is also not a molecular ion because it consists of only one atom.

Helium is a noble gas and does not readily form covalent bonds with other atoms to create a molecule. 

Explanation

The pressure of oxygen inside a bomb calorimeter is typically 20-40 atmospheres or 20-40 bar,

It is equivalent to 2026.5 to 4053 kPa or 2.0265 to 4.053 MPa.

This high pressure ensures complete combustion of the sample being tested. 

Explanation

At STP, 1 mole of any gas occupies 22.4 dm³.
If 11.2 dm³ = 0.5 mole →
0.5 mole of nitrogen (N₂) = 14 g
→ Full mole = 28 g (molecular mass of N₂)

Explanation

• Iron-59 is used in studies of iron metabolism and the proper functioning of red blood cells (RBCs).
• It is a radioactive isotope that helps trace the movement and utilization of iron in the body.

Explanation

• Liquids take the shape of a container because they have a fixed volume but no fixed shape.
• They conform to the shape of the container they are placed in.

Explanation

• About 75% of elements in the periodic table are metals.
• The periodic table is divided into metals, nonmetals, and metalloids. 
• The classification of elements as metals, nonmetals, or metalloids is based on their physical and chemical properties.

Explanation

• A buffer solution is a mixture of a weak acid and its conjugate base, or a weak base and its conjugate acid, that resists changes in pH when an acid or base is added to it.
• This is because the acid and its conjugate base (or the base and its conjugate acid) react with the added acid or base to maintain the equilibrium, keeping the pH constant.

Explanation

When a chemical cell's voltage drops to zero, it typically indicates that the cell reaction has reached equilibrium.

Explanation

The increase in length (or volume) of solids when heated is specifically called thermal expansion.

Key Information:

Thermal Expansion:

• Occurs due to increased atomic vibrations with temperature.
• Linear expansion: Change in length (e.g., railroad tracks expanding in summer).
• Volumetric expansion: Change in 3D dimensions (e.g., mercury in thermometers).