Which of the following equations will be satisfied by irrotational flow of an incompressible fluid ?

1. $\frac{\delta u}{\delta x}+ \frac{\delta v}{\delta y}+\frac{\delta w}{\delta z}=0$

2. $\frac{\delta u}{\delta y}+\frac{\delta v}{\delta x}=\frac{\mathrm{\delta <\; <div\; class="questions">\; <ul\; class="ul">\; <li>\; <div\; class="option\_section">\; <div\; class="options">\; <ul\; class="ul">\; <li>\; <label\; class="radio">\; <span\; class="option\_no">1</span>\; <div\; class="answer">\; <p>3\; and</p>\; </div>\; </label>\; </li>\; <li>\; <label\; class="radio">\; <span\; class="option\_no">2</span>\; <div\; class="answer">\; <p>1\; and\; 2</p>\; </div>\; </label>\; </li>\; <li>\; <label\; class="radio">\; <span\; class="option\_no">3</span>\; <div\; class="answer">\; <p>1\; and\; 3</p>\; </div>\; </label>\; </li>\; <li>\; <label\; class="radio">\; <span\; class="option\_no">4</span>\; <div\; class="answer">\; <p>1\; and\; 4</p>\; </div>\; </label>\; </li>\; </ul>\; </div>\; </div>\; </li>\; </ul>\; </div>\; <!--end\; question\; details-->\; <hr>\; <h4>Display\; Comments</h4>\; <hr>\; <h4>Leave\; a\; comment</h4>\; <p>Login\; at\; first\; then\; you\; can\; submit\; comment.\; Click\; <a\; href="https://civilhunt.com/login">here</a>\; to\; login.</p>}}{}$