Explanation

In a stationary wave, the particle velocity at a node is zero.

Nodes are points of zero displacement in a stationary wave, and therefore, they do not oscillate and have no velocity. 

Explanation

The substance with the most moles is 3.8 g of H2O (0.211 moles).

Therefore, it has the largest number of molecules. 

Explanation

During means کے دوران

The fire alarm rang during yesterday's meeting.

کل کی میٹنگ کے دوران فائر الارم بج گیا۔

Explanation

He goes to college daily in time.

The subject "He" is third person singular, so in the present simple tense, we add -s to the verb. 

The sentence describes a habitual action, so the present simple tense is appropriate.

Explanation

For 2p orbitals, the principal quantum number (n) is 2.

The azimuthal quantum number (l) for a p-orbital is 1.

So, n = 2, l = 1 is correct.

Explanation

"Damnation means لعنت" means eternal punishment or being condemned

Condemnation means مزمت

Explanation

He had his breakfast at 9 o’clock.

The sentence refers to a specific time in the past ("at 9 o’clock"), so the correct tense is simple past.

"Had" is the simple past tense of "have," and it fits well with a completed past action at a specific time.

Explanation

I hope they will not have left the city before I reach there.

مجھے امید ہے کہ میرے وہاں پہنچنے سے پہلے وہ شہر چھوڑ کر نہیں گئے ہوں گے۔

The sentence talks about a future action ("before I reach there") 

Future completed action is the future perfect:

will not have + past participle

"Will not have left" shows:

A completed action in the future

That you hope they are still there when you arrive

Explanation

As of the most widely accepted recent estimates, about 2.13 million species have been formally described by scientists.

This number includes:

• Animals (insects, mammals, birds, etc.)

• Plants

• Fungi

• Protists

• Bacteria and archaea (though many microbes remain undescribed)

Explanation

Parvoviruses are among the smallest DNA viruses, with a typical diameter of around 18–26 nanometers (nm).

So, 20 nm is the most accurate option from your list.