67-year-old Nath, a nine-term MP, was administered the oath at a simple function in the Rashtrapati Bhavan which was attended by Prime Minister Narendra Modi, Vice President Hamid Ansari, Parliamentary Affairs Minister M Venkaiah Naidu and Minister of State (Parliamentary Affairs) Santosh K Gangwar.
The former Parliamentary Affairs Minister and Lok Sabha Member from Madhya Pradesh's Chhindwara was congratulated by the President and other dignitaries after the oath that took place in the 'Yellow Drawing Room' of the Presidents' House.
After the oath, Nath said that his party will play the role of a "constructive Opposition" and will work to live up to the aspirations of the youth and the country.
"We will certainly play the role of a constructive Opposition. The BJP created ruckus and did riot in the last five years in the House but we will not allow this," Nath told media persons after the oath.
He said the role of the Opposition will be to attract government's attention towards the needs of the people and to help "clear pending legislations."
Nath said the Speaker of the Lok Sabha will decide the Leader of the Opposition and this would happen on Friday.
"It is a important decision to have a Leader of Opposition," he added.
The Protem Speaker performs the duties of the office of the Speaker from the commencement of the sitting of the Lok Sabha till the election of the Speaker.
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