NOVELTY - The process comprises reforming (204) a natural gas stream by steam in presence of a nickel-based catalyst carried out within a controlled temperature to form a product mixture of hydrogen and natural gas such that the product mixture is free from carbon monoxide, removing excess steam from the product mixture, purifying (202) the natural gas stream, preheating (201) the natural gas stream by the product mixture, and generating (203) steam by feeding a water stream to a firebox, supplying a slip stream of the natural gas stream to the firebox and burning the slip stream of the natural gas.    USE - The process is useful for production of a mixture of hydrogen and natural gas such as methane, which is useful as a fuel in automobiles.    ADVANTAGE - The process ensures economical, efficient and easy production of the mixture of hydrogen and natural gas with low level of nitrogen oxide emission and without hazardous to the environment and any impurities.    DETAILED DESCRIPTION - The process comprises reforming (204) a natural gas stream by steam in presence of a nickel-based catalyst carried out within a controlled temperature to form a product mixture of hydrogen and natural gas such that the product mixture is free from carbon monoxide, removing excess steam from the product mixture, purifying (202) the natural gas stream, preheating (201) the natural gas stream by the product mixture, generating (203) steam by feeding a water stream to a firebox, supplying a slip stream of the natural gas stream to the firebox and burning the slip stream of the natural gas in the firebox to heat the water stream to produce the steam, adjusting (206) a composition of the product mixture by analyzing the product mixture and supplying an additional quantity of natural gas to the product mixture to obtain a final product gas mixture having a predefined composition, and recycling (207) a portion of the final product gas mixture based on an outflow demand of the product mixture. The reforming step is carried out at a temperature of 350-390 degrees C, a pressure of 5-7 bars and a gas hourly space velocity on dry basis of 1500-2250 hr-1. The slip stream is supplied by controlling a flow rate of the slip stream based on a temperature in the reformer. An INDEPENDENT CLAIM is included for a plant for production of a mixture of hydrogen and natural gas.    DESCRIPTION OF DRAWING(S) - The diagram shows a flow chart of a process to produce the mixture of hydrogen and natural gas.    Preheating natural gas (201)    Purifying natural gas (202)    Generating steam (203)    Reforming natural gas by steam (204)    Separating excess steam (205)    Adjusting a composition (206)    Recycling a portion of product mixture. (207)