You can enable it from the Plugins option. Q2A is providing this plugin OOTB now with name as reCaptcha. You have to create Key and Secret for the same.
To create Key and Secret :- https://www.google.com/recaptcha/admin
" You can enable it from the Plugins options. Q2A is provide plugin OOTB this now with name is reCaptcha . You must create Key and Secret for same."
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