In cyclic photophosphorylation there is no requirement of external source of electrons.

Explanation:

In photosynthesis, the light-dependent reactions occur in the thylakoid membrane of the chloroplasts. These reactions involve the absorption of light energy by chlorophyll and the conversion of this energy into chemical energy in the form of ATP and NADPH. The light-dependent reactions consist of two main processes: the cyclic electron transport chain (ETC) and the non-cyclic ETC.

1. Cyclic ETC in stroma:
- The cyclic electron transport chain occurs in the stroma lamellae of the chloroplast.
- It involves the flow of electrons from photosystem I (PSI) to the cytochrome complex and back to PSI.
- This process generates ATP through the phosphorylation of ADP, but no NADPH is produced.
- In this process, an external source of electrons is required. The electrons are provided by the splitting of water during the non-cyclic ETC.

2. Photochemical phase in stroma lamellae:
- The photochemical phase of photosynthesis occurs in the stroma lamellae of the chloroplast.
- It involves the absorption of light energy by chlorophyll and the subsequent excitation of electrons.
- These excited electrons are transferred through a series of electron carriers, including photosystem II (PSII) and photosystem I (PSI), resulting in the production of ATP and NADPH.
- In this process, an external source of electrons is not required. The electrons are provided by the chlorophyll molecules themselves.

3. Non-cyclic ETC in chloroplast:
- The non-cyclic electron transport chain occurs in the thylakoid membrane of the chloroplast.
- It involves the flow of electrons from photosystem II (PSII) to photosystem I (PSI) and ultimately to NADP+ to produce NADPH.
- This process also generates ATP through the phosphorylation of ADP.
- In this process, an external source of electrons is required. The electrons are provided by the splitting of water during the light-dependent reactions.

4. Light reaction in stroma:
- The light reaction in the stroma refers to the light-independent reactions, also known as the Calvin cycle or the dark reactions.
- These reactions occur in the stroma of the chloroplast and involve the fixation of carbon dioxide and the production of glucose.
- The light-independent reactions do not require an external source of electrons, as they primarily rely on the ATP and NADPH produced during the light-dependent reactions.

Conclusion:
The correct answer is option B, as the photochemical phase in stroma lamellae does not require an external source of electrons. The electrons are provided by the chlorophyll molecules themselves, which get excited by the absorption of light energy.