Google chief Sundar Pichai has faced accusations of political bias from US politicians.
Mr Pichai was being quizzed by members of the House Judiciary Committee about the way his tech firm runs it business.
Google was accused of having "programmed" bias against conservative views into its algorithms.
Mr Pichai denied the accusation saying he had "issues" with studies that claimed to show the firm's search results excluded right-wing views.
He was asked by Democrat committee member Zoe Lofgren why, when she googled the word "idiot" under images, a picture of President Donald Trump came up.
In response, Mr Pichai explained that keywords were matched against billions of page results and ranked for relevance, popularity and how other people are using the word.
Republican committee member Lamar Smith said conservative voices were being "muted" via Google's search results.
"Such actions pose a grave threat to our democratic form of government," he said.
"This does not happen by accident, it is baked in to the algorithms."
Mr Pichai said independent studies had not uncovered any bias and added that his business was "transparent" about the way its search results were generated.
"We evaluate our studies and our research results," said Mr Pichai.
"We have a wide variety of sources, from both left and right."
He added that it was "impossible" for any individual or group of individuals to manipulate its algorithms.
In response to a further question about perceived bias, he said: "I'm confident we don't approach our work with any political bias."
He added: "It's important that we look at outcomes and assess that there's no evidence of bias."
Mr Pichai was also asked about the work Google was doing in China on the controversial "dragonfly" project.
This is believed to be a search engine drawn up under the oversight of the Chinese government that would censor topics at the behest of the regime.
Mr Pichai said "the number of engineers on the project have varied over time, but at one point we had over 100 people working on it", in response to questioning from Republican committee member Keith Rothfus.
Democratic committee member Sheila Jackson Lee suggested the work could "censor a Chinese person's lifeline to democracy".
She asked: "How can you do that?"
In response, Mr Pichai said: "Right now we have no plans to launch in China. We don't have a search product there.
He said all efforts were "internal" and did not currently involve discussions with the Chinese government.
"Our core mission is to provide users with access to information and getting access to information is an important human right," said Mr Pichai. "We are always compelled across the world to try hard to provide that information."
In response to further questions, Mr Pichai said the company would be "fully transparent" with politicians if the company released a search service in China.
Mr Pichai was questioned extensively about the amount of information that Google collected and what it did with the "mountains" of data it gathered.
The Google boss said many times that it gave people "choices" about the types of data it collected and that it regularly reminded people about their privacy settings.
He said 20 million people a day adjusted their privacy settings to change the types of information they let Google amass.
Mr Pichai had been under growing pressure to testify after he snubbed an earlier hearing called by the Senate Intelligence Committee.
Executives from Facebook and Twitter attended the September event where they faced tough questions.
In a document released before his testimony, Mr Pichai paid tribute to staff at Google and said it had worked to "empower people around the world, especially in the US".
The Congressional session comes the day after the search giant announced that it was shutting down its Google+ social network.
The decision came after it found a vulnerability that could have exposed data on 52.2 million users.