To answer this question, you need to understand the naming of meter unit system. The unit pm stands for pico meter which was 1/1000 of nanometer. Then, the calculation would be:
Number of atom= container length / atom diameter
Number of atom = 25 nm x (1000pm/nm) / 144pm= 173.6 atom
Answer: b. One atom transferring electrons to another atom
Explanation: An ionic bond is formed when an element completely transfers its valence electron to another element. The element which donates the electron is known as electropositive element and the element which accepts the electrons is known as electronegative element. This bond is formed between a metal and an non-metal.
Covalent bonds are formed by sharing of electrons between non metals
For example, In calcium iodide the one electron from calcium metal gets transferred to iodine atom and thus form an ionic bond to give 
Electronic configuration of calcium:
![[Ca]=1s^22s^22p^63s^23p^64s^2](https://tex.z-dn.net/?f=%5BCa%5D%3D1s%5E22s%5E22p%5E63s%5E23p%5E64s%5E2)
Calcium atom will lose two electron to gain noble gas configuration and form calcium cation with +2 charge.
![[Ca^{2+}]=1s^22s^22p^63s^23p^6](https://tex.z-dn.net/?f=%5BCa%5E%7B2%2B%7D%5D%3D1s%5E22s%5E22p%5E63s%5E23p%5E6)
Electronic configuration of iodine:
![[I]=1s^22s^22p^63s^23p^64s^23d^{10}4p^5](https://tex.z-dn.net/?f=%5BI%5D%3D1s%5E22s%5E22p%5E63s%5E23p%5E64s%5E23d%5E%7B10%7D4p%5E5)
Iodine atom will gain one electron to gain noble gas configuration and form iodide ion with -1 charge.
![[I^-]=1s^22s^22p^63s^23p^64s^23d^{10}4p^6](https://tex.z-dn.net/?f=%5BI%5E-%5D%3D1s%5E22s%5E22p%5E63s%5E23p%5E64s%5E23d%5E%7B10%7D4p%5E6)
E = hf
c = speed of electromagnetic wave, c ≈ 3 * 10⁸ m/s,
Planck's constant h = 6.63 *10⁻³⁴ Js
h = Planck's constnat, Frquency, f = c/λ = (3*10⁸)/(488*10⁻⁹)
E = hf
E = hc/λ
E = (6.63 * 10⁻³⁴ * 3 * 10⁸) /(488 * 10⁻⁹)
Energy, E ≈ 4.0758 * 10⁻¹⁹ Joules.
Answer:
The strongest force that exists between molecules of Ammonia is <em>Hydrogen Bonding</em>.
Explanation:
Hydrogen Bond Interactions are those interactions which are formed between a partial positive hydrogen atom bonded directly to most electronegative atoms (i.e. F, O and N) of one molecule interacts with the partial negative most electronegative atom of another molecule.
Hence, in ammonia the nitrogen atom being more electronegative element than Hydrogen will be having partial negative charge and making the hydrogen atom partial positive. Therefore, the attraction between these partials charges will be the main force of interaction between ammonia molecules.
Other than Hydrogen bonding interactions ammonia will also experience dipole-dipole attraction and London dispersion forces.
