Explanation

A metastable state is an excited state of an atom or molecule that has a significantly longer lifetime compared to other excited states, but is still shorter than the ground state.

This means that an electron in a metastable state can stay in that state for a relatively long time before transitioning back to a lower energy level. 

Explanation

Species facing imminent extinction are called endangered.

Specifically, an endangered species is at very high risk of extinction soon, either globally or within a specific region. 

Explanation

A calorimeter is an instrument used to measure the amount of heat absorbed or released during a chemical reaction or physical change.

It is essential for studying thermodynamic properties 

Explanation

 Prokaryotic cells lack membrane-bound organelles like chloroplasts.

Chloroplasts are organelles found in eukaryotic cells, specifically plant cells, and are responsible for photosynthesis.

Prokaryotic cells, while simpler in structure, do possess other components such as"

• Ribosomes (for protein synthesis)
• A cell wall (for structural support)
• DNA (although not contained within a nucleus) 

Explanation

Energy and work have the same dimensional formula, $$[ML2T−2][ML^2T^{-2}]

Both represent the ability to perform work or cause a change in energy.

Explanation

The magnitude of i · (j × k) is:

This is a scalar triple product, and for standard unit vectors:

i · (j × k) = 1

Explanation

The law of conservation of momentum states that the total momentum of a closed system (such as a system of two bodies) remains constant over time, as long as there are no external forces acting on the system.

This means that the total momentum before a collision is equal to the total momentum after the collision.

Explanation

The organelle that is not present in animal cells is the Plastid. 

Plastids, including chloroplasts, are organelles specific to plant cells and are not found in animal cells. 

Endoplasmic Reticulum:

Present in both animal and plant cells. 

Ribosome:

Present in all cells, as they are the site of protein synthesis. 

Mitochondria:

Present in most animal cells, responsible for generating energy. 

Explanation

 The phrase "at time" means "precisely" or "exactly" when used with the verb "arrive."

So, "the train always arrives at time" means the train always arrives on schedule, without any delays.

Explanation

 In the human body, there are 3 pairs of false ribs on each side, corresponding to the 8th, 9th, and 10th pairs of ribs.

These ribs do not directly connect to the sternum (breastbone) like the true ribs (pairs 1-7).

Instead, their cartilage connects to the cartilage of the 7th rib, which is a true rib.