The concentration of reducing agent has great effect on the NPs size, using high concentration of reducing agent, produce small size NPs while Low concentration will produce larger size.

for further study visit below article :

DOI: 10.1002/adma.201800702

Yes but it depend on the concentration of the reductant,temperature and time of the reaction

The concentration of reducing agent effects the size of the nano-particles. Although on increasing the concentration size of nano-particles reduces but it is to the certain extent after that level of optimal concentration reaction it may starts increasing again.

This fact is well stated and proved experimentally for the synthesis of gold nano-particles by Kim et al. in their publication (attached).

@Rishabh Jain, in addition to this, Reducing agents influence the size and shape of nanoparticles, since they define the pressure of the reaction, during their decomposition.

If the reaction pressure is high, the reaction rate is greatly accelerated, and the process of nucleation and growth of the nanoparticles will be highly accelerated,and the opposite effect will occur if the pressure is low, thus prepared nanoparticles have various shapes and sizes.

Please check these reviews

Shape-Controlled Synthesis of Gold and Silver Nanoparticles(Science 2002: Vol. 298 no. 5601 pp. 2176-2179 )

Seed-mediated growth approach for shape-controlled synthesis of spheroidal and rod-like gold nanoparticles using a surfactant template. Advanced Materials, 13(18), 1389.

Shape‐Controlled Synthesis of Metal Nanocrystals: Simple Chemistry Meets Complex Physics?. Angewandte Chemie International Edition, 48(1), 60-103.